The effects of cigarette smoking on the central nervous system can be assessed directly using the electroencephalogram (EEG). Nicotine withdrawal and subsequent replacement have been studied, but have produced conflicting effects on brain electrical activity. We studied the effect of smoking 2 cigarettes at subjects' own pace in 20 subjects. EEG was recorded using the EEGSYS program in the eyes-closed awake state using a bipolar montage. Delta power decreased in central-posterior head regions. Theta power and power in the lower half of the alpha band decreased. Beta power and power in the upper half of the alpha band increased significantly over frontotemporal head regions. Examination of spectra underlying the usual frequency bands revealed that many effects of smoking on EEG power probably resulted from a shift of the overall power spectrum toward higher frequencies, rather than resulting from alterations in activity in specific frequency bands.