Six normal adults were administered an oral dose of 0.25 mg/kg of dextroamphetamine, and their learning performance on a paired-associate task and drug blood level were measured at hourly intervals for 5 hours postdrug intake. Dextroamphetamine plasma concentration peaked at 2 to 3 hours following the oral dose, and learning errors were lowest during the same period. A self-report measure of mood also yielded findings consistent with peak plasma concentration. Similar findings obtained with hyperactive children treated with methylphenidate (Ritalin) lead the authors to conclude that the paired-associate learning task may be useful as an indicator of psychostimulant plasma levels, as a predictor of clinical response after an acute dose, and as a highly controlled task for studying psychostimulant drug effects on learning.