An enzyme linked immunosorbent assay (ELISA) was used to evaluate the prevalence and disease associations of antibodies to a range of negatively charged phospholipids in 111 patients with systemic lupus erythematosus (SLE). The frequency of one or more isotypes of different antiphospholipid antibodies (APLs) was similar (range 33%-45%). When individual isotypes were considered alone there was considerable variation (range 5%-32%). There were significant associations between thrombosis, thrombocytopenia, and central nervous system (CNS) disease but not abortion with elevated APL. Strong associations were found between raised anti-ds-DNA (Farr assay) and a positive direct Coomb's test with raised APL. Thus, APLs are common in SLE and are associated with discrete clinical and laboratory features. However, detection of antibodies to a range of negatively charged phospholipids added little clinically useful information to that obtained by measuring anticardiolipin antibody (ACL) alone. We cannot recommend the use of APLs other than ACL for routine testing.