The development of invertebrate and fish tissue cultures, the characterization and application of new cell lines for the evaluation of physiological and endocrinological cell parameters, cell differentiation, gene expression and pathological and microbiological problems are treated in detail. New techniques for the production of specific proteins in vitro are described. Highlights derive from results of studies on the molecular mechanisms of gene regulation using DNA mediated gene transfer techniques, on the influence of ecdysterone on the differentiation of embryonic cells, and on metabolic processes of cells in culture leading to the identification of functions for individual ribosomal proteins. Data on the establishment of new cell lines, their simplified culture media, and on the special use of cell cultures for the evaluation of the cytotoxicity, accumulation, and metabolization of insecticides are discussed.