Three patients were recently treated for thrombotic thrombocytopenic purpura (TTP). One presented with toxic shock syndrome; TTP developed but promptly responded to a regimen of antiplatelet agents, steroids and plasma exchange. In another the manifestations of TTP developed after presentation with hypertension and abdominal pain. This patient responded to a similar regimen but required extended treatment before remission could be maintained with medications alone. In the third patient the full TTP syndrome appeared after several days of plasma exchange treatment for hemolyticuremic syndrome. He did not respond. It is suggested that TTP may present in many forms initially, that microangiopathic hemolysis may be a late manifestation and that the optimal therapy is not known.