Genetic polymorphism of GC (vitamin D-binding protein) in human urine was revealed by isoelectric focusing and immunoblotting on thin-layer polyacrylamide gels containing 2 M urea. Urine samples from 530 unrelated Japanese from the Fukui district, being only 1-2 ml of original urine, were examined, and correct GC typing was achieved by comparison with the results of direct grouping using plasma. Six common and twelve rare phenotypes were observed. The frequencies of the genes were 0.473 for GC*1F, 0.241 for GC*1S, 0.254 for GC*2, and 0.032 for the total of six rare alleles.