The study was designed to determine the acetylator status in patients with systemic lupus erythematosus (SLE) and compare it to a matched group of healthy volunteers. Disease severity was determined using the revised American College of Rheumatology criteria for classification and the SLE disease activity index. After an overnight fast, each participant received a single oral dose of 100 mg dapsone. After 3 hours, plasma dapsone/monoacetyldapsone ratio was determined. In the control group, frequency of slow acetylators was 73.3%; frequency of rapid acetylators was 26.7%. In SLE patients, frequency of slow acetylators was 78.0%; frequency of rapid acetylators was 12.0%. However, 8.0% were non-acetylators (monoacetyldapsone not detected in plasma). There was no association between acetylator status and severity of SLE.