The kinetics of accumulation and elimination of d- and l-fenfluramine (F) and norfenfluramine (NF) have been studied in 8 young healthy volunteers given daily doses of 60 mg of sugar-coated tablets of 20 mg dl-F hydrochloride (dl-F) t.i.d. and capsules of 15 mg d-F hydrochloride (d-F) b.i.d. for 15 days. Repeated doses of d-F plus l-F gave the same values for the parameters measured as did d-F administered alone. Steady-state concentrations of all compounds were achieved within 4-8 days. The predicted mean steady-state concentrations of d-F and elimination half-lives calculated from the results of a previous single dose study were similar to those measured at steady state in this study, confirming the lack of effect of the drug on hepatic microsomal enzymes and on kinetics after repeated dosing. d-NF concentrations were approximately half those of the parent drug and the half-life was almost twice as long. Steady state concentrations both of L-f and l-NF were consistently about 40-50% higher than of the d-isomers and there was a comparable in the half-life.