2:073-079, 1982.Female rats, anaesthetized with hexobarbital, regained their righting reflex more rapidly following electrostimulation than sham-treated controls. The extent of the decreased sleeping times in these animals varied according to the frequency (cycles per second) of the electrostimulation applied. The frequency which produced the largest decrease in sleeping time was 10 Hz. Determination of the activity of some microsomal enzymes indicated that the decreased sleeping time was not the result of increased hepatic enzyme activity. Animals which had received prior treatment with naloxone exhibited increased sleeping times following barbiturate administration, but the effects of electrostimulation on the sleeping time at 10 Hz was diminished, while the effect of electrostimulation at high frequency (500 Hz) was enhanced. Although repeated daily administration of hexobarbital progressively decreased sleeping times for all the animals, electrostimulation decreased the sleeping times of the treated rats by a similar percentage of the control animals on each successive day. Electrostimulation at a frequency of 10 Hz produced a significant decrease in serum corticosterone levels, whereas 500 Hz resulted in an increase.