Effects of the novel competitive N-methyl-D-aspartate (NMDA)-receptor antagonist SDZ EAA 494 were investigated on memory and attention in humans. SDZ EAA 494 was administered either as single doses at a dose range of 1-50 mg, or as multiple doses over the course of 1 week at doses of 25 mg once or twice daily. Selected cognitive functions were assessed at baseline, 2 and 4 h after single dose administration, and at baseline, 2, 4 and 8 h on days 1 and 7 of multiple dose administration. The assessments included simple and complex reaction time tests to assess attention, and verbal, non-verbal and spatial memory tests with immediate and late recall. Verbal and non-verbal memory test performance was significantly impaired at a dose level of 50 mg after single administration, and of 25 mg twice daily after multiple administration, without concomitant significant impairment of reaction time. Spatial memory test performance was not significantly affected. The maximum effect occurred 2 h postmedication and was more pronounced after repeated administration. These results suggest that the inhibition of NMDA-receptors in humans may impair memory processes.