In 52 conceptuses with known genomic origin, HLA determination was performed on whole villi and/or stromal cell cultures. In 26 androgenetic, diploid conceptuses, one or two paternal HLA-A,B haplotypes were found; twenty-four triploid conceptuses with two paternal and one maternal chromosome sets showed either one maternal and one paternal haplotype or one/two paternal HLA-A,B haplotypes. Consequently, androgenesis could not be demonstrated by lack of maternal antigens alone. Concomitant expression of three HLA haplotypes was not seen. HLA-A2 was passed on to the conceptus, both in the genetic subgroups and in the entire series, more frequently than expected.