This volume is based on the proceedings of a NATO-Gulbenkian Foundation sponsored Summer School held in May-June 1982 in Sintra­ Estoril, Portugal. Given the accelerated growth of knowledge in the field of eukaryotic gene expression, it seemed timely to hold a NATO Advanced Study Institute to discuss current developments in this area of biology and to evaluate the potential of emerging technologies such as gene transfer, recombinant DNA cloning and quantitative high resolution two-dimensional gel electrophoresis. The initial articles in t~is volume describe various differentiation models and address questions such as the relationships between differentiation and cell proliferation, biochemical changes accompanying differen­ tiation, expression of differentiated