Trophic characteristics of neuroprotectors cerebrolysin and semax were evaluated by their capacity to induce differentiation and improve survival of cultured rat pheochromocytoma (PC12) cells. Morphological signs of cell differentiation (enlargement and formation of processes) were seen 24 h after addition of cerebrolysin into culture medium. Cerebrolysin improved survival of PC12 cells in serum-free medium. In a concentration of 100 mug/ml cerebrolysin decreased the content of apoptotic cells from 32% (control) to 10%. Semax produced no trophic effect on PC12 cells. hence, the neuroprotective effect of cerebrolysin in vivo probably results from trophic activity, while the protective effects of semax are mediated by other mechanisms.