The influence of cocaine, amphetamine, cathinone, pargyline and nomifensine on inward calcium current was studied using internally perfused neurons of the snail Lymnaea stagnalis. While nomifensine and pargyline inhibited inward calcium current in the concentrations 10(-7)-10(-4) M and did not affect them in the concentrations 10(-9)-10(-8) M, cocaine, amphetamine and cathinone had a biphasic action on inward calcium current, causing activation (10-30 percent) at 10(-9)-10(-7) M, and inhibition at higher concentrations. Only cathinone caused a shift of the I-V characteristics of the membrane along the potential axis. It is suggested that drugs of abuse affect membrane excitability and inward calcium current in neurons directly.