Kava (Piper methysticum) and alcohol were administered either separately or in combination to human subjects. Self-reports of their levels of impairment and intoxication were collected, and performance skills on a number of cognitive and visuomotor tests were determined, before and three times after consumption of the experimental drink. Kava alone had no effect on reported condition. In contrast, alcohol produced marked changes in each of the five subjective measures, all of which were in the direction of lowered ability. The combination of these two substances produced even larger negative changes on these measures. In the cognitive tests, kava produced a decrement in performance on Digit Symbol Coding. Alcohol produced a significant decrease in performance on a divided attention test, which was almost entirely on the peripheral, discontinuous component of the test. The combination of kava and alcohol produced an even greater decrease in performance on this test, and in the same component. The present findings suggest that kava alone has little effect on reported condition and cognitive performance, but appears to potentiate both perceived and measured impairment when combined with alcohol.