In the present study PCR primers were designed for detecting all known DPA1 variability, i.e., the presently recognized six DPA1 alleles 0103 to 0401, and also for separation of the four DPA1*02 alleles, by PCR amplification with sequence-specific primers (PCR-SSP). For each sample seven different PCR reactions were performed which allowed the identification of all DPA1 alleles and the resolution of all DPA1 genotypes. Forty-eight cell lines and 100 donor spleen cells were investigated by the DPA1 PCR-SSP technique. In the forty-eight known workshop cell-lines no false positive or false negative results were obtained. The 100 donor spleen cells were only typed by the PCR-SSP technique and in their DNAs only one or two DPA1 alleles were found. Twenty cell lines and twenty donor spleen cells were typed on two separate occasions and interpreted blindly. The reproducibility between the repeated typings was 100%. The length of the specific products ranged from 103 to 258 base pairs and the amplification patterns obtained were easy to interpret. In conclusion, DPA1 typing by the PCR-SSP method is an accurate typing technique with high sensitivity, specificity and reproducibility. Analysis of the distribution of DPA1 alleles was performed in 100 Caucasian samples, 100 African samples and 80 Oriental samples, including separation of the four of HLA-DPA1 alleles. Each ethnic group appeared to have one (Caucasians), or two (Africans and Orientals), frequent DPA1 allele(s) and a high frequency of DPA1 homozygotes, suggesting that, like for the DPB1 locus, balancing selection does not appear to be affecting the evolution of the DPA1 locus.