The effects of age and sex on spontaneously occurring spike-wave complexes in rats of the WAG/Rij strain were studied in 2 experiments. In the first study, 3 independent groups of male rats were tested; the first group at 75 days old, the second at 140 days and the third at 245 days. In the second study, males as well as females were repeatedly tested at the ages of 75, 125 and 175 days. Both experiments indicated an increase with age in the number of spike-waves complexes and in the number of rats with absences. In the second experiment there were no differences detected between males and females at any of the ages. Similarities to and differences with human absence epilepsy are discussed and it is once more concluded that this particular inbred strain may be useful as an additional model of absence epilepsy.