Investigations have been performed in 80 couples with unexplained recurrent spontaneous abortions and no live birth (1 degree RSA), as well as in 33 couples with unexplained RSA following one live birth (2 degrees RSA), compared with control couples with no history of repeated early pregnancy failure. A significant bias towards a family history was given for 1 degree RSA women. Elevated total serum IgE levels and tissue-reactive autoantibodies were not significantly more prevalent in the RSA groups, and both 1 degrees and 2 degrees RSA patients had a similar incidence of serum lymphocytotoxic antibody. HLA typing indicated a trend towards parental HLA sharing which did not achieve clear significance at any locus, whereas there was significant apparent HLA-B locus homozygosity for 1 degree RSA women. An elevated prevalence of HLA-A2, B12 haplotypes was also noted for 2 degrees RSA, which may indicate some form of linkage disequilibrium in this population. These results, overall, did not provide evidence to identify a major subgroup of unexplained RSA patients.