A rapid and specific proton magnetic resonance (PMR) spectroscopic method was developed for determining ketoprofen in capsules. Mandelic acid was used as the internal standard and DMSO-d(6) served as the PMR solvent. Undeuterated DMSO was also used as a solvent and good results were obtained since the resonance signals of ketoprofen and mandelic acid used in the analysis did not interfere with the signal and side bands of DMSO. The concentration of drug per unit dose was calculated from the integral values for the resonance signals of ketoprofen at 1.40 ppm and mandelic acid at 5.10 ppm. The average recovery value for ketoprofen in synthetic samples was 100.16 +/- 0.03% (SD) with a coefficient variation of 0.03%. The method using commercial products gave comparable results to those obtained by the method of BP 1993.