The present paper describes three studies examining the acute effects of single doses of Ginkgo biloba (GK501), Ginseng (G115) and their combination (Ginkoba M/E, Pharmaton SA) on the performance of healthy young adults (mean age 21 years) during serial arithmetic tasks with differing cognitive load. In each double-blind, placebo-controlled study three different treatment doses and a placebo were administered, according to a balanced crossover design, with a 7-day washout period between each dose. Participants' scores on two computerised serial subtraction tasks (Serial Threes and Serial Sevens) were assessed pre-dosing and at 1, 2.5, 4 and 6 h thereafter. A number of significant time, dose and task-specific effects were associated with each treatment. There was a dose-dependent improvement in speed of responding during Serial Threes following Ginkgo biloba. Different doses of Ginseng improved accuracy and slowed responses during Serial Sevens. The most striking result, however, was a highly significant and sustained increase in the number of Serial Sevens responses following 320 mg of the Ginkgo-Ginseng combination at all post-treatment testing times. This was accompanied by improved accuracy during Serial Sevens and Serial Threes following the 640 mg and the 960 mg dose, respectively. The paper concludes with speculation into the possible mechanisms underlying these effects.