The basal 45Ca2+ influx into resting human blood lymphocytes was measured. This process showed biphasic kinetics with first rapid phase followed by the second long-lasting and markedly slower phase. Further, it showed signs of saturability and reaches maximal values at 37 degrees C and extracellular pH 7.2. The basal 45Ca2+ influx was stimulated by addition of submicromolar concentrations of 4 beta-phorbol-12-myristate-13-acetate, and this effect was abolished by protein kinase C (PKC) inhibitor Ro-31-8220. In the regulation of basal 45Ca2+ influx is probably only partially involved adenylate cyclase pathway as show results with intracellular c-AMP elevating agents (dB-c-AMP, 3-isobutyl-1-metylxantine and forskolin). Uncoupler 3,3',4',5-tetrachloro-salicylanilide (TCS) in micromolar concentrations stimulated basal 45Ca2+ influx and its effect was more significant in media with high extracellular concentration of K+.