1. The acetylator phenotype was determined for 142 Nigerian adults by administering sulphamethazine (40 mg/kg body wt) and analysing six hour urines for free and acetylated drug.

2. Of these 142 subjects, 21 (14.8%) had no red cell glucose 6-phosphate dehydrogenase activity, 35 (24.6%) had partial activity and 86 (60.56%) had normal activity.

3. The percentage of slow acetylators among the three groups was 38.1%, 40 and 40·7% respectively. The differences between the three groups were not statistically significant. However, individuals with no red cell glucose 6-phosphate dehydrogenase activity and who are also slow acetylators may be more sensitive to the effects ot drugs like sulphamethazine, dapsone and isoniazid.