The relative bioavailability and pharmacokinetic profiles of Oramorph SR (OSR) and MST Continus (MST), were evaluated by a randomized, four-way cross-over study in 24 healthy, male volunteers given single oral (30 mg) doses whilst fasting or after a high-fat breakfast. Mean Cmax, tmax, AUC (0,24h), AUC and tlag were significantly greater in fed compared with fasting subjects. Overall relative bioavailability of the two formulations (log AUC), was within the acceptable 80-125% limits for bioequivalence both fed and fasting. Mean fasting Cmax for OSR was greater than MST (P < 0.05) but there was no difference between formulations in mean fed Cmax. No statistically significant difference between OSR and MST was found for other parameters nor in the incidence of adverse events. These results suggest that OSR and MST are bioequivalent and that if patients were to transfer between formulations, dosage adjustment would be unnecessary, irrespective of their meal schedules or food intake.