The effect of various treatments on acetylation status measured by caffeine metabolites was investigated in 17 subjects with non-insulin dependent diabetes mellitus (NIDDM). The test drugs, caffeine (200 mg), antipyrine (20 mg/kg) and coumarin (5 mg), were given simultaneously, and urinary 5-acetylamino-6-formyl-amino-3-methyluracil/1-methylxanthine (AFMU/1X) molar ratio was measured before and after 8 weeks of therapy. The urinary AFMU/1X molar ratio decreased (p