The relative ability of cocaine, tropacocaine and amphetamine to inhibit the uptake of [3H]norepinephrine (NE), [3H]dopamine (DA) and [3H]5-hydroxytryptamine (5HT) was examined in whole brain synaptosomes from BALB, C3H, C57BL and DBA inbred mouse strains. With inhibition of [3H]NE uptake, synaptosomes from BALB and C57 mice were substantially more sensitive to cocaine inhibition than those from DBA or C3H. Moreover, with BALB and C57 tissue, amphetamine was as potent as cocaine, whereas with C3H and DBA, amphetamine and tropacocaine were much less potent inhibitors of [3H]NE uptake. With respect to [3H]DA accumulation, synaptosomes from BALB, C57 and DBA were equally sensitive to cocaine inhibition, while C3H synaptosomes were significantly less sensitive. In each of the four strains, amphetamine was more potent than cocaine, and tropacocaine far less potent. The relative potencies of the three drugs varied significantly among the four strains. With [3H]5HT accumulation, synaptosomes from DBA were exquisitely sensitive to cocaine inhibition, followed by BALB and lastly by C57 and C3H. In each of these strains, amphetamine and tropacocaine were equipotent at [3H]5HT inhibition, and less potent than cocaine. The results suggest that there are pronounced genetic differences in sensitivity to monoamine uptake inhibition by cocaine, which may arise from genetic differences in either carrier topology or other site of cocaine interaction. The results further suggest that genetic behavioral differences to cocaine and amphetamine may involve complex neurotransmitter interactions.