SYNOPSIS.The expression of intracellular patterning is perhaps nowhere more impressive than in the arrangements of structural elements associated with the cell surface in protozoa. The view is proposed that biochemical studies of protozoan plasma membranes and associated surface structures represent important contributions of potential significance for the understanding of the perpetuation, and expression of positional information at the intracellular level. Some recent work dealing with the isolation, identification, and metabolism of pellicular proteins inTetrahymenais presented and discussed. Some integral membrane proteins have been identified by iodination and polyacrylamide gel electrophoresis. Labeling studies suggest heterogeneous turnover rates within the group of presently identified membrane proteins. High molecular weight proteins with some similarity to spectrin have been isolated fromTetrahymenaepiplasm. It is suggested that the ciliate epiplasm is one example of membrane‐associated, actomyosin‐like systems found in a variety of cell types. The epiplasm may play a role in the positioning of surface‐associated structures and in the control of cell