Restriction fragment length polymorphism (RFLP) of Ha-ras gene was surveyed by Southern blot analysis in leukocyte DNA from 55 normal individuals and 58 urothelial cancer patients in Japan. Three common alleles and 4 rare alleles were classified. The frequency of common alleles in normal Japanese individuals differed from that in Caucasians previously reported; a 7.2-7.5-kb BamHI fragment of common allele was not observed in Japanese individuals. No significant increase in frequency of the rare Ha-ras allele was observed in the group of cancer patients. Moreover, no significant difference in frequency was observed for the 3 common alleles. Tumor DNA was compared with leukocyte DNA in 30 urothelial cancer patients: in 3 of 8 cases with heterozygous Ha-ras locus, decreased intensity of one band, indicating partial loss of one allele in tumor DNA, was observed. In 3 tumors with either deletion of one Ha-ras allele or a rare Ha-ras allele, expression of Ha-ras gene was examined by Northern blot analysis. Such genetic alterations did not always result in a marked increase in Ha-ras expression. These data suggest that these genetic alterations are not directly related to Ha-ras expression, and that RFLP of Ha-ras gene is not a useful genetic marker for urothelial cancer. On the other hand, deletion of one Ha-ras allele was observed in 1 of 5 cases of bladder cancer and in 2 of 3 cases of renal pelvic cancer, suggesting that that deletion may be important in the development of urothelial cancer.