A cytologic study of an occupational cohort at increased risk for bladder cancer was conducted. The cohort consisted of 542 workers who were potentially exposed to beta-naphthylamine (91598), benzidine (92875), alpha-naphthylamine (134327), and o-toluidine (119937) between 1949 and 1972 at a dye intermediary production facility at Augusta, Georgia. A previous study had found an excess risk of bladder cancer in the cohort. Two urine samples were collected from each subject for a urine cytology examination. The cytological findings were classified as positive, suspicious, atypical, or negative. Subjects with positive, suspicious, or atypical cytologies were referred to a urology clinic for diagnostic study which included repeat urinalyses for cytological examination, bladder washings analysis, cytoscopy, and multiple directed and random bladder biopsies. Six subjects had positive and two suspicious urine cytologies. One of the positive subjects had a previous history of bladder cancer. Biopsies indicated invasive carcinoma or in-situ nonpapillary carcinoma in five positive subjects. Severe atypia was found in the sixth subject. No significant abnormalities were found in the two subjects with suspicious cytological findings. Fifty six subjects had atypical urine cytologies. Fifty three of these were diagnosed from urine samples only; the other three required bladder washings. A total of 165 single and multiple biopsies were performed on these subjects. Of these, three had normal urothelium or hyperplasia, 11 atypia, one had carcinoma in-situ, and one had a noninfiltrating papillary carcinoma. A total of 477 subjects had normal cytological findings. One of these developed symptoms 5 months later. Biopsy revealed a papillary transitional cell carcinoma invading the lamina propria. The authors conclude that close observation of the cohort is indicated as the workers can be expected to develop more cancers in the future.