In 52 conceptuses with known genomic origin, the HLA types expressed on whole villi and/or stromal cell cultures were compared with the HLA types of the patients. No preference for either HLA compatibility or incompatibility was found for androgenetic and paternally derived triploid conceptuses as a whole. Heterozygous, androgenetic, conceptuses, however, showed a trend towards preferential incompatibility, which may be of importance for their apparent greater risk for trophoblastic tumour. HLA antibodies were found in 19.2% of the women, i.e. in the range reported for molar as well as non-molar pregnancies. Non-HLA antibodies reacting with lymphocytes of the spouse and/or cells from the conceptus were observed.