Structure-function relationships in membranes have been studied extensively correlating spin labeling and transport phenomena in terms of their response to temperature (in bacteria). These studies are being extended by x-ray diffraction and monolayer physical chemistry. The studies are also being expanded into animal systems where we are now able to regulate the degree of saturated fatty acid content in the membrane lipids, and can consequently define changes of state in animal cell surface membranes. The effects of lipid phase transitions in animal cells are being studied not only on transport, but also upon lectin binding and lectin mediated cell agglutination. This will allow for testing a number of current models for agglutination by lectins. Studies are being continued on the mechanism of assembly of bacterial membranes. Previous studies indicate that new domains of membrane containing newly formed lipids can be formed and exist as stable and separate entities under rigorously controlled conditions. These studies are being extended to test the hypothesis that newly synthesized proteins (and most likely only integral proteins) are incorporated with the newly synthesized lipid domains in a coupled fashion.