The effect of lindane on 45Ca fluxes in synaptosomes was examined to determine whether modulation of calcium regulation can explain the lindane-induced enhancement in neurotransmitter release observed in other preparations. Lindane (0.03 - 4.6 microM) enhanced calcium uptake in non-depolarizing (low K+) medium: the effect was maximal at 0.1 microM lindane, which increased uptake by 15.8%. Lindane (11.5 microM) decreased calcium uptake in depolarizing (high K+) medium; lower concentrations were ineffective. In addition, lindane (9.2 microM) increased early 45Ca release from synaptosomes. However, lindane (2.4 or 5.9 microM) had no effect on calcium uptake by lysed synaptosomes in the presence or absence of mitochondrial poisons and/or ATP, indicating that lindane does not affect sub-cellular calcium storage. It is concluded that the lindane-induced changes in synaptosomal calcium flux are due to an increase in non-specific synaptic membrane permeability to calcium.