Summary. Four cases are reported in which a bleeding disorder associated with a long bleeding time and a low factor-VIII level, like von Willebrand's disease, appears to have developed in adult life. In each there were abnormalities of plasma proteins, similar to but in some instances more extreme than patterns found in haemophilia and ‘classical’ von Willebrand's disease. One patient's bleeding tendency developed in association with a generalized illness, probably systemic lupus erythematosus, and improved rapidly on steroid treatment. The other three patients, with no symptoms of underlying disease, were not treated with steroids. Two patients, infused with plasma, showed rather more than the predicted rise in factor VIII.