Imipramine was taken up by rat cerebellar neurons in primary culture. The process was dependent on time, temperature and pH and was reduced in the presence of the adenosine triphosphatase (ATPase) inhibitor dicyclohexylcarbodiimide or in the absence of glucose. Uptake approached saturation at 100 microM imipramine where approximately 42 nmol of the drug accumulated intracellularly per mg cell protein. Propranolol, but not serotonin, competed for imipramine uptake and uptake was inhibited by the 'lysosomotropic' amine chloroquine and by the Na+/H+ ionophore monensin, both of which dissipate proton gradients. Neurons were fractionated on Percoll gradients and the fractions exposed to [3H]imipramine. MgATP-dependent accumulation of [3H]imipramine was found mainly in fractions enriched for dense lysosomes. We conclude that imipramine was taken up by cerebellar neurons in primary culture and accumulated at high concentrations in intracellular compartments.