Platelet transfusions are an important supportive measure during treatment for acute nonlymphocytic leukemia (ANLL). The presence of splenomegaly may produce decreased posttransfusion platelet increments leading some to recommend an increased dose of platelets per transfusion in this situation. Forty-nine newly diagnosed patients with ANLL were evaluated during 1980 and 1981, and 24% had palpable splenomegaly. Although treated with usual doses of platelets per transfusion, there was no detectable statistical increase in transfusion requirement or incidence of hemorrhage in patients with splenomegaly. Experimental evidence indicates that the splenic platelet pool enlarges with splenomegaly, but the life span of circulating platelets is not significantly changed. Furthermore, the splenic platelet pool is in dynamic equilibrium with the circulating platelet pool thus allowing these platelets to participate in hemostasis. Although posttransfusion increment in platelet count may be less, it appears that platelet transfusion therapy need not be altered solely because of splenomegaly.