1. Isolated, non-identified neurons were voltage clamped using the internal perfusion technique. 2. Ions of Ag+ (1-100 microM) introduced into the bathing solution activated a steady-state inward current (IAg) in the soma. The effect of Ag+ was reversible when the concentration of Ag+ was less than 75 microM or the time of application was shorter than 10 min. 3. IAg was observed both in the presence and absence of Na+ ions in the extracellular saline. It could also be activated when Cs+ ions were substituted for Na+ ions. 4. The current-voltage characteristics were linear in the voltage range -100 to 0 mV. The reversal potential in control saline was an average of 1.19 +/- 5.1 mV. 5. The application of Ag+ ions induces an elevation of intracellular free Ca2+ concentration by 10-20 times in both Ca(2+)-containing and Ca(2+)-free extracellular salines, as revealed by Fura-2 measurements. 6. Agents that increase the intracellular free Ca2+ concentration ([Ca2+]i), like thymol, caffeine and dinitrophenol, increased the amplitude of IAg. The effect was additive. Ruthenium Red, which blocks the release of Ca2+ from intracellular stores, decreased the Ag+ effect. 7. It is concluded that extracellularly applied Ag+ ions increase the cytoplasmic free Ca2+ concentration, which in turn activates non-specific cationic channels. 8. Ag+ ions in 1-10 microM concentration were able to decrease the voltage-activated Ca2+ current amplitude. This decrease, however, was due to the increase of [Ca2+]i which caused Ca(2+)-dependent inactivation.