Acetylator phenotype has been determined using sulfamethazine in 109 patients histologically diagnosed with colorectal carcinoma (resected in 74 patients by the time of the study) and in 96 age-matched controls. Fifty-five % of patients and 58.3% of controls were classified as slow acetylators (chi 2 = 0.11, not significant). No differences were observed in the distribution of acetylator phenotype when analyzing separately male and female, surgically treated and untreated, and colonic and rectal carcinoma patients. We conclude that acetylator polymorphism is not a genetic trait related to the risk of developing colorectal carcinoma in human beings.