Transgenic animals - a new era in developmental biology and medicine; determination of retroviral mutation rates using spleen necrosis virus-based vectors and helper cells; steroid hormone receptors as transactivators of gene expression; targeted mutagenesis in embryo-directed stem cells; application of germ line transformation to the study of myogenesis; regulation of expression of genes for mild proteins; a normally silent gene of the transgene mouse major urinary protein comples is functional in transgenic mice; the activation and silencing of gene transcription in the liver; gene targeting embryonic stem cells; a human multidrug-resistant cDNA (MDR1) under the control of the beta-actin promoter confers drug resistance in the bone marrow of transgenic mice; insertion of a disease resistance gene into the chicken germline; analysis of regulatory genes using the transgene mouse system; regulation of expression of a class 1 MHC transgene; generation of transgenic mice with major histocompatibility class II genes; mice transgenic for a gene that encodes a soluble, polymorphic antigen from the major histocompatibility complex; principles of gene transfer and the treatment of disease; transgenic mice carrying HIV proviral DNA; high levels of human apolipoprotein A-1 in transgenic mice result in increased levels of high-density lipo-protein cholesterol; effects of human growth hormone on reproductive and neuroendocrine functions in transgenic mice; enhanced growth performance in transgenic swine; production of sheep transgenic for growth hormone genes; production of transgenic cattle by pronuclear injection; methods for the introduction of recombinant DNA into chicken embryos; gene transfer in fish; studies on transgenic fish; gene transfer, expression and inheritance; transgenic rats - a discussion; patenting of animals.