Normal and tumorous nephrectomy specimens from seven renal cell carcinoma patients were subjected to a Southern analysis using chromosome #3-specific polymorphic probes. Three patients were not informative because of homozygosity at all loci studied. One patient showing heterozygosity at 3q in normal tissue had a tumor that remained heterozygous. In three patients the tumor showed loss of heterozygosity for a short arm marker at 3p21. In one of them heterozygosity for a second short arm marker was also lost. Another of these three patients retained heterozygosity for this second short arm marker, as well as for a long arm marker, suggesting a chromosomal breakpoint between the loci for the two short arm markers. Our results demonstrate that the known involvement of a short arm region of chromosome #3 in the development of renal cell carcinoma can readily be further evaluated by direct molecular methods.