A patient with clinical and laboratory evidence of disseminated intravascular coagulation associated with deep-vein thrombosis and pulmonary embolism developed a qualitative platelet abnormality characterized by a defective release reaction. Second-phase aggregation induced by ADP and adrenaline was impaired, and reduced collagen-induced aggregation was accompanied by defective release of ADP and ATP. The decrease in total platelet ATP and ADP, the high ATP:ADP ratio in the presence of normal amounts of metabolic adenine nucleotides, and the low content of serotonin associated with abnormal uptake and metabolism of the exogenous amine suggested that the defective platelet function was due to lack of the platelet organelles in which serotonin and nonmetabolic adenine nucleotides are normally stored. Acquired storage pool disease is likely to be related to exposure of circulating platelets to aggregating agents, with their degranulation occurring during disseminated intravascular coagulation.