We observed the alpha-sleep pattern in 6 out of 44 subjects who offered neither somatic nor psychological complaints. All of the 6 subjects demonstrated the pattern consistently over a period of several years. 14 of the polygraphic sleep EEGs were recorded when free of any drugs, 10 after administration of benzodiazepine hypnotics. The alpha-sleep pattern is superimposed on all the regular patterns during any of the different sleep stages, and shows a cyclic representation with an increase correlating to the delta-sleep stages 3 and 4. It can be differentiated from other activities due to its localization, frequency characteristics, occurrence in relation to different sleep stages, and modification under the influence of benzodiazepine hypnotics. In contrast to the sigma-spindle activity, the alpha-sleep pattern is reduced with these drugs. Regarding the functional significance of the alpha-sleep pattern one might consider the possibility that it indicates a partially heightened level of sleep depth.