The pharmacokinetics of nimesulide (4-nitro-2-phenoxymethane-sulfonanilide, NMS), a non-steroidal antiinflammatory drug, and of its 4-hydroxy metabolite (4-nitro-2-(4'-hydroxy-phenoxy)-methane sulfonanilide, OH-NMS) was studied after a single oral dose (200 mg) and after repeated treatments (100 mg every 12 hours for 7 days) of NMS to two groups of 12 healthy volunteers. Plasma concentrations of NMS and OH-NMS were followed for 48 hours after the single dose and up to the 12th hour on the 1st day and on the 7th day during repeated treatment. After the single dose of 200 mg peak plasma concentrations of the drug (9.85 micrograms/ml) were reached at 3.17 hours and the half-life during the elimination phase was 4.95 hours. The metabolite reached highest plasma levels (3.03 micrograms/ml) at 5.33 hours and its apparent half-life was similar to that of the parent drug (4.78 hours). NMS plasma levels on the 7th day, predicted from the results of the 1st day, were similar to the measured values. The pharmacokinetics of NMS or OH-NMS after single or repeated dose was not time or dose dependent.