The effects of oral d-amphetamine 5-30 mg on human social and verbal behavior were studied using repeated observations within subjects under a time-sampling observation procedure in a residential research ward. d-Amphetamine increased socializing in all three subjects studied, but only increased standing in one of the subjects. In the second experiment throat microphones and voice-operated relays were used to measure automatically quantitative aspects of dyadic verbal interactions during 1-hr daily sessions. Total speaking time showed dose-related increases in 5 of the 7 subjects receiving d-amphetamine. Adjective checklist self-report scores indicating stimulant drug effects were as sensitive and reliable as the speaking measure to the effects of d-amphetamine in these subjects. Speaking time also increased in 2 of the 8 partners who received placebo when the subjects with whom they were paired received d-amphetamine. This represents a socially mediated indirect drug effect. Adjective checklist scores of the partners receiving placebo were not changed when the paired subjects received d-amphetamine. Under controlled experimental conditions the naturalistic human behaviors of socializing and speaking are sensitive dependent variables for behavioral pharmacology research.