Introduction: G.R. Wilmot and S.T. Warren, New Mutational Basis of Disease. Fragile X Syndrome: R. Hagerman, Clinical and Diagnostic Aspects of Fragile X Syndrome. G. Imbert, Y. Feng, D.L. Nelson, S.T. Warren, and J-L. Mandell, FMR 1 and Mutations in Fragile X Syndrome: Molecular Biology, Biochemistry, and Genetics. B.A. Oostra and P.J. Willems, Murine Model of Fragile X Syndrome. Other Fragile Sites: D.L. Nelson, FRAXE Mental Retardation and other Folate-Sensitive Sites. T. Glover, Common Fragile Sites. Spinal and Bulbar Muscular Atrophy: J.D. Zajac and H.E. MacLean, Kennedys Disease: Clinical Aspecs. D.E. Merry and K.H. Fischbeck, Genetics and Molecular Biology of the Androgen Receptor CAG Repeat. Myotonic Dystrophy: P. Harper, Myotonic Dystrophy as a Trinucleotide Repeat Disorder--A Clinical Perspective. J.D. Waring and R. Korneluk, Genetic Studies of the Myotonic Dystrophy CTG Repeat. H.F. Epstein and S. Jin, Biochemical Studies of the DM Protein Kinase (DMPK). C.L. Winchester and K.J. Johnson, Is Myotonic Dystrophy (DM) the Result of a Contiguous Gene Defect? D.G. Monckton, T. Ashizawa, and M.J. Siciliano, Murine Models for Myotonic Dystrophy. Dentatorubral-Pallidoluysian Atrophy: I. Kondo, Clinical Aspects of DRPLA. S. Tsuji, Molecular Genetics of Dentatorubral-Pallidoluysian Atrophy (DRPLA). J. Vance, The Allelic Variant: HAW River Syndrome. Spinocerebellar Ataxia Type 1: S.H. Subramony and P.J.S. Vig, Clinical Apsects of SCA-1. B.T. Koshy, A. Matilla, and H.Y. Zoghbi, Genetic Studies of the SCA1 Gene and Biochemical Work of the Ataxin. D. Kaytor and H.T. Orr, Murine Model of SCA1: Repeat Instability and Neurobiology. Other Dominant Spinocerebellar Ataxias: S-M. Pulst, Spinocerebellar Ataxia Type 2. G. David, N. Abbas, A. Durr, G. Stevanin, G. Cancel, C. Yvert, G. Imbert, F. Saudou, J-L. Mandel, Y. Agid, and A. Brice, Autosomal Dominant Cerebellar Ataxia with Macular Dystrophy (SCA7) is Caused by a Highly Unstable CAG Repeat Expansion. M. Nakamoto, H. Ikeda, and A. Kakizuka, Genetic and Molecular Studies of Machado-Joseph Disease. Huntington's Disease: R.H. Meyers, K.S. Marans, and M.E. MacDonald, Huntington's Disease. A.H.M. Mahbubul Huq, A. Hackam, R.K. Graham, C.L. Wellington, and M.R. Hayden, Molecular Pathogenesis of Huntington Disease: Biochemical Studies of Huntington. G.P. Bates, E.E. Wanker, and S.W. Davies, Murine Models of Huntington's Disease. Freidreich's Ataxia: M. Pandolfo and M. Koenig, Clinical and Pathological Aspects of Freidreich Ataxia. Candidate Disorders Revealing Anticipation: M.G. McInnis and R.L. Margolis, Anticipation and Psychiatric Diseases. A.D. Paterson, D.M.J. Naimark, J.B. Vincent, J.L. Kennedy, and A. Petronis, Genetic Anticipation in Neurological and Other Disorders. Approaches to Detect Unstable Trinucleotide Repeat Loci: R.L. Margolis and C.A. Ross, Detection of Unstable Trinucleotide Repeat Loci: Genome and cDNA Screening. M. Schalling, K. Lindblad, Q-P. Yuan, C.E. Burgess, C. Zander, and T. Hudson, RED Technology. Y. Trottier, G. Zeder-Lutz, and J-L. Mandel, Selective Recognition of Proteins with Pathological Polyglutamine Tracts by a Monoclonal Antibody. K. Sanpei and S. Tsuji, DIRECT Technologies. Systems for the Study of Genetic Instabilities: A. Bacolla, R.P. Bowater, and R.D. Wells, Systems for the Study of Genetic Instabilities: Escherichia coli. S. Jinks-Robertson, C. Greene, and W. Cheng, Genetic Instabilities in Yeast. P. Steinbach, D. Wohrle, D. Glaser, and W. Vogel, Systems for the Study of Triplet Repeat Instability: Cultured Mammalian Cells. P.M. Glazer, S.E. Andrew, F.R. Jirik, and L. Narayanan, Genetic Instability in Transgenic Mice Deficient in DNA Mismatch Repair. E.P. Leeflang, S. Tavare, P. Marjoram, R. Grewal, C.O.S. Neal, and N. Arnheim, Human Germline Mutation Analysis by Single Genome PCR: Application to Dynamic Mutations. Biophysical and Structural Studies on Triplet Repeat Sequences: R. Gellibolian and A. Bacolla, Biophysical and Structural Studies on Triplet Repeat Sequences: Duplex Triplet Repeat Structures. C.E. Pearson and R.R. Sinden, Slipped Strand DNA, Dynamic Mutations, and Human Disease. X. Gao, X. Huang, G.K. Smith, and M. Zheng, Structure and Dynamics of Single Stranded Nucleic Acids Containing Trinucleotide Repeats. S.V. Santhana-Mariappan, X. Chen, P. Catasti, E.M. Bradbury, and G. Gupta, Structural Studies on the Unstable Triplet Repeats. J.D. Griffith and Y-H. Wang, Nucleosome Analyses and Diseases of Chromatin Structure. Replication-Repair of TRS: S.H. Wilson, R.K. Singhal, and B.Z. Zmudzka, Studies of DNA Polymerases in Replication-Based Repeat Expansion. L.C. Kroutil and T.A. Kunkel, DNA Replication Errors Involving Strand Misalignments. K. Ohshima and R.D. Wells, In Vitro DNA Synthesis of Triplet Repeat Sequences. Oligoglutamine Effects: H. Green and P. Djian, Amino Acid Repeats in Proteins and the Neurological Diseases Produced by Polyglutamine. C.A. Ross, R.L. Margolis, M.W. Becher, J.D. Wood, S. Engelender, and A.H. Sharp, Pathogenesis of Polyglutamine Neurodegenerative Diseases: Towards a Unifying Mechanism. Genome Instability Not Involving Triplet Repeats: S.E. Antonarakis, Expansion of a 12-mer (CCCCGCCCCGCG) Repeat in Progressive Myoclonus Epilepsy. J.M. Cunningham, L.A. Boardman, L.J. Burgart, and S.N. Thibodeau, Microsatellite Instability in Sporadic and Hereditary Non-Polyposis Colon Cancers. Overview and Summary: R.D. Wells and S.T. Warren, Future Directions. Subject Index.