Recently, I have established a cell culture system, using dissociated cells from immature chicken testis, that consists of steroidogenic and fibroblastic cells. In suspension cultures, the cells reaggregate as do many embryonic cells. In monolayer cultures, the steroidogenic cells reorganize into discrete colonies; their behavior is similar to that of Leydig cells in developing chick testis in vivo. I have also demonstrated that the steroidogenic cells are in fact androgenic and also contain specific intercellular matrix materials shown to be glycoproteins. Using labelled precursors, I shall investigate the synthesis of these cell surface-associated materials while the testicular cells are undergoing reaggregation and reorganization in vitro. The major experimental tools include chromatography and autoradiography. Enzyme-substrate specificities will also be employed to explore further the nature of the intercellular materials. The effect of several antibiotics of known biological action on the synthesis of cell surface components will be investigated. Since my results indicate that there may be two pathways involved in the production of testosterone in monolayer cultures, I wish to determine whether or not there is a preferred, or a change of, pathway during different developmental behavior of the cells in vitro. Labelled progesterone and other intermediates in the two pathways will be used to study the kinetics of their conversion to testosterone in an effort to answer the question posed above. Since the testicular cell culture system shows two important developmental phenomena, i.e., cell-type specific surface materials and specific hormone production, it is then pertinent to investigate the intimacy of these two parameters. I wish not only to elucidate cell-interactions in relation to testosterone biosynthesis but also the role of androgenic cells in the initiation and regulation of spermatogenesis. The proposed work is relevant to biomedical problems of great importance: birth control and testicular tumor formation.