The pharmacokinetic properties of ibuprofen p.o. given either as a lysine salt or as acid to eight young, healthy male volunteers was investigated. Ibuprofen lysinate, administered after overnight fasting, produced peak plasma concentrations significantly earlier and higher than ibuprofen acid. A similar difference was observed when the drugs were given following a standardized breakfast. Under these conditions the lat-time was significantly shorter for the lysine salt than for the acid. The pharmacokinetic differences are likely to result from the faster dissolution rate of ibuprofen lysinate. They indicate that the administration of ibuprofen as lysine salt before meals may be advantageous if rapid and reliable onset of pain relief is required.