In order to investigate the possible mechanisms underlying platelet functional changes in patients affected by neoplasms, platelet lipid composition, plasma beta-thromboglobulin (Beta-TG) and serum thromboxane B2 (TXB2) were investigated in 16 male patients affected by pulmonary carcinoma and in 16 comparable control subjects. In patients high levels of plasma Beta-TG (67 +/- 9 versus controls 14 +/- 4 ng/ml, p < 0.001) and serum TXB2 (434 +/- 56 versus 223 +/- 48 ng/ml, p < 0.001) were observed. Also platelet lipid composition was found altered in patients with respect to controls (lower percent levels in n-3 fatty acids and in linoleic acid esterified in the main platelet phospholipid fractions: at least p < 0.05). These results indicate that in vivo platelet activation is detectable in neoplastic patients and it is associated with alterations in platelet lipid composition. In the light of the important role played by membrane lipids in platelet functions related to thrombosis and haemostasis we conclude that platelet lipid changes could cooperate in platelet activation and increased thrombotic risk so frequently observed in neoplastic disease.