A new method of automated sleep-wake staging in the rat is described. Hippocampal electroencephalographic (HPC) and nuchal electromyographic signals were recorded by a digital polygraph. The HPC channel was filtered off-line to obtain the original plus theta and delta waves. Statistics of each of these four channels were obtained every 5 s and exported to a standard spreadsheet. The automated staging consisted of five steps: (1) automatic detection of waking, nonrapid eye movement sleep and rapid eye movement sleep patterns (5-s periods); (2) calculation of statistics for each vigilance state; (3) final classification of 5-s periods; (4) construction of a primary 20-s epoch hypnogram; and (5) automatic refinement of the previous hypnogram. The system includes indices about the accuracy of the staging and was validated with five recordings of 23 h each. The global agreement between human and automatic scoring in the validation recordings was 94.32%.