The study objective was to compare the bioavailability of codeine and ibuprofen after oral administration of the two drugs alone or in association. The study was performed in three different periods, each separated by a wash-out of 6 days. Plasma concentrations were measured in 24 healthy volunteers after administration of a single oral dose of codeine phosphate (25 mg) and/or ibuprofen (200 mg). Codeine and ibuprofen assays were performed using two different HPLC methods. The relative bioavailabilities of codeine and ibuprofen (alone or in association) were 106 +/- 24% (mean +/- sd) and 101 +/- 19%, respectively. The results obtained demonstrated that bioavailabilities of codeine and ibuprofen were not modified when the two drugs were administrated alone or in association.