The effect of a single dose of 4 sugar-coated tablets of Cosaldon (1-hexyl-3,7-dimethylxanthine (pentifylline) + nicotinic acid) was shown by quantitative pharmaco-EEG investigations and psychometric tests in 12 volunteers aged 58 to 75 years, who were in a good physical condition. The design was randomized, double-blind and cross-over designed against placebo. EEG and psychometric tests were made before medication and repeated each hour up to 6 h after medication. Each turn was split up into a resting-EEG (R-EEG) and a vigilance-EEG (V-EEG) lasting 3 min each; the psychometric tests were made immediately afterwards. An increase of the vigilance, shown by an increased EEG-power, was found after Cosaldon administration as compared to placebo. Furthermore, the delta and theta intensity decreased to a statistically significant degree, while the intensity within the alpha-1-scope increased. The strongest effect as compared to placebo could be observed 4 h after medication. The statistical significance was shown for the V-EEG-condition, the R-EEG showed only minor changes. The effects in the occipital region were stronger than in the more frontal parts. In accordance with the results of the EEG, the psychological tests showed remarkable improvements in performance which reached their maximum between 2 and 4 h after medication.