Epidemiologic studies have revealed an increased risk for development of transitional cell carcinoma (TCC) among dye workers/painters occupationally exposed to aromatic amines such as benzidine, beta-naphthylamine, orthotoluidine, and aniline. In the present study, p53 gene mutations in 26 patients with bladder lesions occupationally exposed to aromatic amines were examined by single-strand conformation polymorphism analysis of PCR-amplified DNA segments, followed by direct sequencing. All were male, and age at admission ranged from 43 to 75 (median 66) years. Twenty-nine biopsy specimens were from primary lesions; 17 (61%) of these lesions were from TCC including one carcinoma in situ (CIS); 11 were from dysplasia; and 1 was taken from normal-looking transitional epithelium adjoining TCC. TCC lesions included 12 with low-grade (Grade 1 or 2) and 5 with high-grade (Grade 3 or CIS) changes. Twenty-four recurrent lesions were biopsied in 16 patients: TCC was found in 12 lesions (50%), CIS in 1 (4%), and dysplasia in 11 (46%). All lesions were localized within the submucosa except for two, which invaded into the muscle layers. PCR-single-strand conformation polymorphism analysis demonstrated that mutations (a) occurred in both dysplasia and in normal-looking epithelium, in addition to TCC lesions; (b) were at different sites in the p53 gene in concurrent or metachronous lesions; and (c) occurred in exon 5 in approximately 70% of lesions, especially at codons 151 and 152. C to T transitions were predominantly seen. These findings clearly show differences in the pattern of p53 mutation in occupational versus nonoccupational bladder lesions. Because both common and unique point mutations were found in p53 in concurrent and metachronous lesions, our results suggest that the multifocality of occupational bladder cancer arises both from multiple clonal lesions (field change) and from the dissemination of a single clone.