We have analyzed HLA data from the UNOS registry on 20,230 patients on the renal waiting list in 1991 and 18,708 donors from 1988-1992. Significant differences were found in the distribution of HLA antigens for comparisons of the total donor pool and the various racial groups of patients as well as for inter- and intraracial comparisons of donors and patients. Within a racial group, the frequencies of blanks and of broad antigens were usually higher in patients while those of splits were usually higher in donors. Comparisons between the total donor pool and the various racial groups of patients showed that the likelihood of mismatch was greater for African-Americans and Hispanics than for Caucasians but that the chance of mismatch is high for all groups and the average number of antigens mismatched will not vary greatly among the different races. Heterogeneity, as measured by the percentage of the population with different phenotypes, was higher in African-Americans (97.2-99.7%) and Hispanics (97.7-99.4%) than in Caucasians (83.3-86.5%) because of multiple occurrences of a few phenotypes, most containing A1, B8 and DR3, in Caucasians. However, the most common phenotypes of Caucasian donors differed from those of Caucasian patients. All phenotypes were rare (0.007-0.61%) and, with the exception of a small group of Caucasian patients, the likelihood of achieving a good match is low, regardless of race. These data explain the observations that, with the exception of the phenotypically identical match, HLA matching does not influence organ distribution significantly.