Rhesus monkeys were chronically implanted with stimulating electrodes at positive reinforcement sites in anterolateral hypothalamus and locus ceruleus. Monkeys were then allowed to roam free in a large cage for six days and deliver brain stimulation to themselves when they wished. No monkey sought stimulation at locus ceruleus after the first few minutes in the cage, but all repeatedly barpressed for anterolateral hypothalamic stimualtion. Barpressing rates in 3 of 4 monkeys were found to correlate significantly with a 40–45 min ultradian rhythm while the rate for the other monkey correlated best with an 85 minute rhythm.