Stromal cells obtained from bone marrow of Wistar rats were cultured in liquid medium. The cultures were divided into control and experimental groups. After 24 h of culture, the medium was removed and replaced by a new one containing 10-6 and 10-9M 4β-phorbol or phorbol 12,13-diacetate ester in the experimental cultures, or phorbol solvent alone in control cultures. After 7 days, the cultures were stained with Wright’s stain or were subjected to cytochemical procedures for demonstration of nonspecific esterase, alkaline and acid phosphatases and diaphorase activities. The obtained results showed that phorbols stimulated proliferation: fibroblast colonies, fibroblasts, macrophages, immature reticular cells. The number of adipocytes was markedly lower in the experimental cultures. Phorbols stimulated activity of the investigated enzymes.