Dopamine interaction with target cells undoubtably involves binding to plasma membrane receptors. However, the well documented cell growth inhibitory activity of this catecholamine suggests nuclear regulation. To evaluate this possibility, we determined the intracellular localization and binding of [3H]dopamine in human retinoblastoma (Y-79 cells), normal mouse fibroblasts (LM-cells), and in the rat uterus. Cytosol and purified nuclear preparations devoid of plasma membrane components contained specific, saturable, high affinity (Kd approximately 20 nM) binding sites for [3H]dopamine. The nuclear binding affinity for dopamine, L-dopa, and L-dopa methyl ester correlated with the inhibitory effects of these compounds on cell proliferation, suggesting that intracellular dopamine binding sites may also be involved in cellular response to catecholamines.