We have studied the HLA-class I and class II antigen distribution in a sample of 75 Spanish Gypsies and 74 Spanish non-Gypsies by serology, restriction fragment length polymorphism, and protein chain reaction and hybridization with allele-specific oligonucleotide probes. When both population samples are compared, we find that Gypsies have a statistically significantly higher frequency of A1, A11, B61, Cw6, DQ5 and haplotypes DR16 DQ5 Dw21 and DR14 DQ5 Dw9 DR52b. Frequency of A3, A29, B44, DR4, DQ2, DQ8 and haplotypes DR1 DQ5 and DR7 DQ2 DB17 DR53 are significantly lower in this ethnic group. The analysis of the serological data in the two populations demonstrates that Cw6 can be split into long Cw6 (Cw6.1) and short Cw6 (Cw6.2). Haplotype A1-Cw6-B61-DR14-DQ5 is the most characteristic in Gypsies, with a frequency of 13%. Estimation of the genetic distances shows that Spanish Gypsies are closer to Indian Caucasoid populations than to the Spanish non-Gypsy population. HLA data support the proposed historical origin of this ethnic group.