Summary:In humans there is a substantial decline in NREM electroencephalographic (EEG) slow-wave activity with advancing age. The present findings show that similar age-related EEG changes occur in the cat. Slow-wave (0.5–4.0 Hz) EEG activity during NREM sleep was compared in six young adult (2–4 years) and six aged (10–12 years) cats of either sex. Computer measures of slow-wave incidence and amplitude disclosed significant age- and gender-related differences. Although old male and female animals were of comparable age, only males showed significant EEG alterations. These consisted of an attenuation of slow-wave amplitude over posterolateral cortex and reductions in both the incidence and amplitude of slow-wave activity over sensorimotor cortex.