Ginkgo biloba extracts (GBE) have been shown to be as effective as anti-cholinesterase inhibitors in improving the cognitive test scores of patients with dementia. Although it has been assumed that GBE works via its antioxidant and vascular effects, some evidence has emerged that GBE may have some pro-cholinergic activity. We wished to test the hypothesis that a standardised preparation of GBE, Li 1370, increases cholinergic activity by measuring its effect on the sleep polysomnogram. In particular, latency to Rapid Eye Movement (REM) sleep is sensitive to cholinergic activity. For this purpose we recruited 10 healthy volunteers of both sexes and recorded sleep polysomnograms in a randomised cross-over study, comparing sleep polysomnograms taken the night after a single evening dose of Li 1370 (240 mg) with sleep polysomnograms taken after an evening dose of placebo. No significant differences in sleep parameters (including REM sleep measures) were detected; however sleep efficiency measures and subjective sleep quality reports showed that Li 1370 was well tolerated.