Baseline studies of 111Indium oxine labelled platelet life-span, platelet alpha-granule release products, beta-thromboglobulin (beta TG) and platelet factor 4 (PF4), and factor VIII related activities were performed on 9 asymptomatic patients with sickle cell disease, who were subsequently randomised in a prospective double-blind trial of ticlopidine (250 mg. b. d.) or placebo for one month and the investigations repeated.