Twenty-four patients with various types of tumors and without evidence of consumption coagulopathy (normal routine coagulation tests) were investigated for intraplatelet ATP, ADP, serotonin, beta-thromboglobulin and platelet factor 4; the percentage of light circulating platelets was also determined. Evidence for an acquired storage pool defect was found in seven patients (29%) without any correlation with the clinical status, the presence of metastases, platelet count or fibrinogen level. These results show that exhausted platelets are commonly encountered in cancerous patients even in the absence of consumption coagulopathy. The precise mechanism of this abnormality remains to be established.