The N-acetyltransferase phenotype was determined in 105 German patients with bladder carcinoma and in a control group of 42 healthy subjects. The slow phenotype was significantly more frequent among the patients (61.9% compared to 42.9% in the control group). Potential risk factors like occupational exposure, smoking habits, drug abuse and urological anamnestic predispositions were evaluated in relation to staging and grading of the disease, and acetylator phenotype.