Since patients who regularly take NSAIDS may use sucralfate because of its cytoprotective properties, we examined the influence of this compound on the pharmacokinetics of diclofenac. Potassium diclofenac (105 mg) was administered orally to eighteen healthy male volunteers with or without a 5-day pre-treatment with sucralfate (2000 mg twice daily). Blood samples were collected at intervals post-dose and serum concentrations of diclofenac were determined by reverse-phase h.p.l.c. Pre-treatment with sucralfate significantly decreased both the AUC(0,8 h) 2265 ng h ml-1 (geometric mean) (range 1815-2827) vs 1821 ng h ml-1 (1295-2562) and the Cmax 1135 ng ml-1 (geometric mean) (range 898-1436) 701 ng ml-1 (501-981) with no significant delay in absorption tmax 1.0 h (median) (range 0.5-2.0) vs 1.0 h (0.5-4.0). The short-term treatment of healthy male volunteers with sucralfate decreases potassium diclofenac bioavailability. These findings suggest that either an appropriate increase in the diclofenac intake or the use of another gastric mucosa protector must be adopted.