Enhanced platelet function, particularly in response to collagen, is a common occurrence in diabetes that increases the risk of cardiovascular disease. Ginkgo biloba extract is ingested primarily to improve mental focus but it possesses a blood-thinning potential, which has not been well characterized. This study was designed to compare the effect of ingesting G. biloba extract on platelet aggregation in platelet-rich plasma (PRP) and prostanoid urinary excretion in healthy volunteers and subjects with Type 2 diabetes mellitus (T2DM). Before and after ingesting 120 mg of standardized G. biloba extract for 3 months, platelet aggregation was studied in PRP and urinary metabolites of thromboxane B(2) (TXB(2)) and prostacyclin (PGI(2)) were measured. In healthy volunteers (age, 42+/-11 years; BMI, 28.4+/-4.8 kg/m(2); n=28), the ingestion of G. biloba extract significantly increased fasting insulin and C-peptide (10+/-4 vs. 12+/-6 microU/ml, p<0.007 and 1.3+/-0.8 vs. 2.1+/-1.1 ng/ml, p<0.001, respectively) and significantly reduced collagen but not PAF-mediated platelet aggregation, converting 21 of 28 subjects with [COL+/EPI+] platelets to the [COL-/EPI+] phenotype. This was accompanied by a reduction of 11-dehydro-TXB(2) from 12.4+/-6.1 to 10.3+/-6.1 ng/mg Cr (p<0.04) and PGI(2) metabolites (2,3-dinor-6-keto-PGF(1alpha) and 6-keto-PGF(1alpha)) from 2.2+/-0.8 to 1.8+/-0.8 ng/mg Cr (p<0.05). In the T2DM subjects (age, 54+/-8; BMI, 36.6+/-7.9 kg/m(2); n=19), G. biloba ingestion did not affect pancreatic beta-cell function but significantly reduced platelet aggregation, converting 16 of 19 [COL+/EPI+] platelets to the [COL-/EPI+] phenotype. Unlike the healthy volunteers, this was not accompanied by a reduced urinary prostanoid excretion. G. biloba-induced reduction of both classes of prostanoid metabolites in healthy volunteers, but not in T2DM subjects, may suggest a nonselective inhibition of COX-1-mediated TXA(2) in platelets and COX-2-mediated PGI(2) production by the endothelial cells and perhaps platelet-enriched levels of arachidonic acid or COX-1 activity, or both, in T2DM subjects.