A variable but often significant proportion of urinary bladder cancer in urban areas can be attributed to occupational and cultural (cigarette smoking) situations associated with exposures to various arylamines. The variable N-acetylation of carcinogenic arylamines by human hepatic enzyme systems, the known genetic regulation and polymorphic distribution of this enzyme activity in humans, and the known enhanced susceptibility of individuals with the genetically-distinct "slow acetylator" phenotype to various arylamine toxicities, has prompted examination of possible correlations between N-acetyltransferase phenotype and urinary bladder cancer risk in rural and urban populations. In this context, N-acetylation is viewed as a component of detoxication pathways with respect to arylamine bladder carcinogenesis. In preliminary utilizations of this approach, a population of urban urinary bladder cancer patients from Copenhagen, Denmark displayed a 13% excess (p = 0.065) of individuals with the slow acetylator phenotype (46/71 = 64.8%) when compared to a Danish control population (38/74 = 51.4%). These data are consistent with the possibility that arylamines may play an etiological role in bladder cancer in this locale and that slow acetylator individuals may be at higher relative risk (1.74) than rapid acetylator individuals. As 95% of patients reported histories of smoking, it was not possible to isolate and examine smoking factors. In contrast, a population of rural urinary bladder cancer patients from Lund, Sweden, where bladder cancer incidence (20/100,000) (1971) is lower than in Copenhagen (43.8/100,000) (1968-72), no difference in slow acetylator distribution was observed between bladder cancer (80/115 = 69.6%) and Swedish control (79/118 = 66.9%) populations, indicating a relative lack of involvement of arylamines in the etiology of rural bladder cancer. Populations of "spontaneous" bladder cancer patients would be expected to contain variable portions of disease related to arylamine exposure and would be less likely to display a detectable correlation than would an industrial population with documentable arylamine exposure. Consequently, confirmation of this hypothesis is being pursued by examination of industrial populations in an effort to obtain an empirical estimate of relative risk for slow and rapid acetylator phenotypes. These studies involve exposure-matched workmen both with and without bladder cancer.