Biochemical studies have shown that the ability of erythrosine to inhibit dopamine uptake into brain synaptosomal preparations is dependent on the concentration of tissue present in the assay mixture. Thus, the finding that erythrosine inhibits dopamine uptake (which, if true, would provide a plausible explanation of the Feingold hypothesis of childhood hyperactivity) may simply be an artifact that results from nonspecific interactions with brain membranes. In addition, although erythrosine given parenterally (50 milligrams per kilogram) did not alter locomotor activity of control of 6-hydroxydopamine-treated rats, erythrosine (50 to 300 milligrams per kilogram) attenuated the effect of punishment in a "conflict" paradigm.