The discriminative stimulus (DS) and subjective effects of d-amphetamine (AMP) were examined in male and female normal healthy adults. Subjects were trained to discriminate between oral AMP (10 mg) and placebo. Of the 100 subjects who underwent discrimination training, 53 reliably learned the discrimination. These "discriminators" (Ds) were compared with the 47 "nondiscriminators" (NDs) on a variety of measures. Ds and NDs did not differ qualitatively in their response to AMP. As a group Ds were more certain than NDs of their ability to discriminate between AMP and placebo and were more accurate in labelling AMP as a stimulant. AMP also had a greater effect for Ds than for NDs on ratings of drug liking and general activity level during the day. Although Ds generally showed a stronger subjective response to AMP, Ds differed significantly from NDs on only 4 of 18 mood scales affected by AMP (2 anxiety scales and analog ratings of "stimulated" and "high"). Ds did not differ from NDs on any of the following measures: body weight, gender, current or lifetime drug use, baseline mood state, subjective response to placebo, or a variety of personality traits. The results demonstrate considerable individual differences in sensitivity to AMP and suggest a relationship between the DS effects of AMP and specific mood states.