Treatment of thrombotic thrombocytopenic purpura (TTP) with cryoprecipitate-poor plasma (cryosupernatant) as substitution liquid has brought a portion of the relapsing forms of this syndrome under control. We experimented the use of plasma exchange (PE) with CPP as plasma substitute in the initial treatment of four patients with TTP at onset, in an attempt to elicit a faster response to therapy. We observed a clinical response in the four patients treated; however, laboratory indices of complete and stable response (platelet count, serum lactate dehydrogenase level) did not normalize in concert with clinical improvement.