Sixty six women with first or second trimester fetal loss were investigated for the presence of lupus anticoagulant by routine coagulation tests and the dilute Russell's viper venom time with a platelet neutralisation procedure, and for raised anticardiolipin antibodies by an enzyme linked immunosorbent assay. Of 35 women with recurrent fetal loss, seven were positive for lupus anticoagulant and six had increased IgG anticardiolipin antibodies, while of 31 women with only one or two episodes of fetal loss, one had lupus anticoagulant and none increased IgG anticardiolipin antibodies. These findings were significantly different. There was no difference in the incidence of increased IgM anticardiolipin antibodies between the two groups (three and two cases, respectively). A further 11 women with intrauterine death in the third trimester were studied and lupus anticoagulant and raised IgM anticardiolipin antibodies were found in one case. No woman was known to have systemic lupus erythematosus. It is concluded that lupus anticoagulant and increased IgG anticardiolipin antibodies are independently associated with recurrent first and second trimester fetal loss and that such cases should be investigated, even in the presence of otherwise good health, by a comprehensive methodological approach.