Cytogenetic studies were successfully carried out in 5 tumor tissues from Japanese patients with nonfamilial renal cell carcinoma, histologically diagnosed as clear cell subtype. Mitotic cells were obtained by a combined method of enzymatic disaggregation and short-term culture (6-12 days). The modal chromosome numbers were found to be diploid or near-diploid in all the cases examined. Every case showed characteristic structural and numerical abnormalities. Rearrangements in the short arm of chromosome 3 were observed as clonal abnormalities in all the cases, including a translocation t(3;6) resulting in a partial loss of 3p (3 cases), a terminal deletion of 3p (one case) and 2 different translocations involving 3p and 8p (one case). The other clonal abnormalities were a whole or partial trisomy of chromosome 7 and a loss of Y chromosome. The overall results in the present study were consistent with those of our previous data in American patients, and suggest that the rearrangements of chromosome 3 leading to a partial loss of its short arm may play primary and significant role(s) in the development of renal cell carcinoma.