A lot of attention has recently been paid to antiphospholipid and antiendothelial cell antibodies as serological markers for systemic autoimmune diseases. Antiphospholipid antibodies appear to display a prognostic value for recurrent thrombosis and fetal loss both in a subset of systemic lupus erythematosus and in patients with the primary antiphospholipid syndrome. The range of diagnostic tests for the antiphospholipid syndrome is now becoming larger with the inclusion of assays suitable for identifying antibodies against phospholipids other than cardiolipin and especially against phospholipid-binding proteins. Antiendothelial cell antibodies have been suggested as serological markers for immune-mediated vascular damage. In vitro and in vivo experimental models as well as epidemiological studies seem to support this. However, the assays for their detection still lack standardization.