Thirty-one patients over the age of 50 years and showing a mild to moderate degree of memory impairment entered a 6-month double-blind, placebo controlled, parallel group design study to assess the effects of a standardized Ginkgo biloba extract (containing 24% flavonoid glycosides and 6% terpenes) on cognitive function. Patients were allocated at random to receive oral doses of 40 mg Ginkgo biloba extract or identical placebo 3-times daily. Assessments were made at baseline and after 12 and 24 weeks of treatment using a range of psychometric tests. Efficacy data were available for 27 patients (15 in the placebo group and 12 in the active treatment group). Statistical analysis of the data as compared to baseline suggests that Ginkgo biloba extract had a beneficial effect on cognitive function in this group of patients. Performance on the Digit Copying sub-test of the Kendrick battery was significantly improved at both 12 and 24 weeks, while the median speed of response on a computerized version of a classification task also showed a significant superiority over placebo at 24 weeks.