We studied dapsone pharmacokinetics in eight children with compromised immune function who were receiving three different preparations. Peak serum concentration was less than 0.25 microgram/ml after doses of an extemporaneous liquid preparation but ranged from 0.72 to 1.33 micrograms/ml after initial tablet or proprietary liquid doses and 1.48 to 2.48 microgram/ml during long-term proprietary liquid administration. Elimination followed first-order kinetics; the mean elimination half-life was 15.1 hours.