We examined Southern blot analyses of normal and tumor DNAs from 50 patients with sporadic renal cancer, using the human L-myc oncogene fragment as a hybridization probe. Our purpose was to study the relationship between the restriction fragment length polymorphism (RFLP) of the L-myc and the frequencies of metastases. There was no individual difference in patterns of L-myc RFLP between normal and tumor-tissue DNAs digested with EcoRI. The patients were classified into 3 genetic types according to the polymorphic patterns defined by the 2 alleles [10-kilobase (kb) and 6.6-kb fragments]. The relative ratios of the 3 genotypes in the renal cancer patients were similar to those seen in healthy Japanese. However, of 16 patients who exhibited distant organ metastases at the time of surgery, only one was a 10-kb fragment homozygote. The incidence of distant metastases in 10-kb homozygotes was significantly lower than that in 6.6-kb homozygotes plus heterozygotes (p = 0.06). These results basically correspond to the previous findings in the lung cancer patients, and suggest that L-myc RFLP is a widely applicable genetic marker to predict prognosis in cancer patients.