A complementary DNA clone for a serotonin (5HT) transporter has been isolated from rat basophilic leukemia cells. The complementary DNA sequence predicts a 653-amino acid protein with 12 to 13 putative transmembrane domains. The 5HT transporter has significant homology to the gamma-aminobutyric acid, dopamine, and norepinephrine transporters. Uptake by CV-1 cells expressing the transporter complementary DNA resembles 5HT uptake by platelets and brain synaptosomes; it is sensitive to antidepressants, amphetamine derivatives, and cocaine.