A major impact of the genetic engineering revolution on modern medicine will depend on the ability to introduce foreign genes into higher eukaryotes and mammalian cells. This symposium will critically examine the development of efficient vectors for gene delivery into cells, tissues, and embryos, with special emphasis on the role of enhancers in tissue specific expression in a variety of model systems, including yeast, Drosophila, amphibian and mouse. There will be in depth discussion of methods for enhancing transduced gene expression and eliciting tissue-specific expression of these foreign genes. Mechanisms for increasing homologous recombination in mammalian cells also will be discussed. A major portion of the meeting will be devoted to understanding the molecular basis of human genetic diseases, including disorders of the urea cycle, purine metabolism, hemoglobins, collagen metabolism and clotting factors, Duchenne muscular dystrophy, and cystic fibrosis. Prospects for somatic cell gene therapy to correct human genetic disorders will be discussed, with special emphasis on bone marrow transplantation and alternate modes utilizing skin cells, fibroblasts or hepatocytes. Finally, a general seminar will review ethical considerations of human gene therapy.