In September 1991, an NIH workshop on molecular and biological aspects of antiphospholipid antibodies (aPL) identified questions for future studies: are the antibodies defined by the ELISA and by the lupus anticoagulant tests the same? Is aPL directly responsible for disease? What is the antigen? What drives the production of aPL? What is the role of beta 2-glycoprotein I? What accounts for patient heterogeneity? Can a satisfactory animal model be developed? The NIH workshop did not address important clinical questions, including those of pathogenesis and treatment. In 1994 many of these questions have at least partial answers. beta 2-glycoprotein I appears to be an obligatory component of the antigen, abnormal coagulation is the probable central pathogenic event and animal models now exist. There are still critical unknowns that define a future research agenda: the genetics of the aPL syndrome, the relationship of aPL to SLE and mechanisms of pathogenesis (including why clotting is episodic and what is the cellular or anatomical location of the initial injury). Despite a decade of clinical studies, risk prediction for defined patient groups is only now beginning to be studied. There are still almost no randomized, prospective, controlled treatment trials on any aspect of the syndrome nor are there definitive answers regarding which among antiplatelet, anticoagulant or antithrombin therapies is superior, what is the role of immunosuppressive therapy and what experimental therapies might be introduced. The molecular biology of the antigen-antibody interaction will soon be fully understood, then the cellular and the organism biology. Definitive treatment interventions may await this understanding but adequate therapies are available at this time to conduct important and effective prospective clinical trials.