Pre-eclampsia is a syndrome with a strong familial component. Autosomal recessive inheritance acting only in the mother is not consistent with the epidemiological data, and a more complex genetic susceptibility, involving interactions between maternal and fetal genomes, seems likely. The human leukocyte antigen (HLA) system has been implicated, but many of the findings reported have been inconsistent or contradictory. Pre-eclampsia is unlikely to be the simple result of excessive HLA-class II antigen sharing between mother and fetus, as was first thought, but a more complex mechanism involving feto-maternal compatibility cannot be excluded. The reported increase in HLA-DR4 in mothers and babies from pre-eclamptic pregnancies has not been independently confirmed for mothers, and no further studies have been conducted with babies. Consequently, the allegedly stronger relationship with HLA-DR4 sharing between mother and fetus has neither been confirmed nor refuted. Certain (B44-DR7)-containing haplotypes appear to confer increased risk for pre-eclampsia on the basis of independent analyses of American and Scottish populations. HLA-DR53 may be associated with the antiphospholipid antibody syndrome, which is itself a strong risk factor for pre-eclampsia. The tumour necrosis factor (TNF)-alpha allele, TNF1, may be associated with pre-eclampsia and certainly elevated concentrations of the cytokine appear to be a feature of the disease. The inducibility of TNF-alpha is HLA-class II-dependent, and the relevance of HLA-class II genes might be entirely in relation to TNF-alpha synthesis and secretion.