The main goal of the present study was to explore electrophysiological differences between lucid and nonlucid dreams in REM sleep. Seven men and four women experienced in lucid dreaming underwent polysomnographic recordings in the sleep laboratory on two consecutive nights. EEG signals were subjected to spectral analysis to obtain five different frequency bands between 1 and 20 Hz. Lucidity was determined by both subjective dream reports and eye-movement signals made by the subjects in response to light stimuli indicating a REM period. The main discrimination factor between lucid and nonlucid dreaming was found in the beta-1 frequency band (13–19 Hz), which in lucid dreaming was increased in both parietal regions. The ratio of frontal to parietal beta-1 activity was 1 to 1.16 in nonlucid and 1 to 1.77 in lucid dreaming. A tendency towards the greatest increase was observed in the left parietal lobe (P3), an area of the brain considered to be related to semantic understanding and self-awareness. Lucid dreaming refers to a specific dream state characterized by the dreamer's awareness of being in a dream and the ability to volitionally control its content. Lucid dreamers report being in possession of all their cognitive faculties: they are able to reason clearly, to remember the conditions of waking life, and to act voluntarily within the dream upon reflection or in accordance with plans decided upon before sleep (Carskadon, 1995). The dream state can be experienced very vividly, and thus lucid dreams are often described as peak experiences or "high" dreams (Tart, 1990).