Behavioral effects of high-peak-power microwave pulses on Wistar rats were studied by operant schedules. Each of twelve rats that had been trained to press a lever to receive food pellets was assigned randomly in groups of four to three different schedules of reinforcement: fixed-ratio (FR), variable-interval (VI), and differential-reinforcement-of-low-rates (DRL). After achieving a steady baseline performance, each animal was exposed for 10 min to 1.25-GHz microwave radiation at 1-MW peak-power (10-microseconds pulse width). Each pulse produced a peak whole-body SA and SAR of 2.1 J/kg and 0.21 MW/kg. Total doses (SAs) were set to 0.50, 1.5, 4.5, and 14 kJ/kg by adjusting the pulse-repetition rate. The corresponding time-averaged whole-body SARs were 0.84, 2.5, 7.6, and 23 W/kg. A microwave-transparent animal holder was used to keep the animal's body axis parallel to the E-field. Exposures at the highest dose caused an average colonic temperature rise of 2.5 degrees C and these animals failed to respond at all for about 13 minutes after the exposure. Their colonic temperatures had decreased to 1.1 degrees C, or less, above their pre-exposure (normal) temperature level when they began to respond. The FR and VI animals failed to reach their baseline levels of performance thereafter, while those on the DRL schedule displayed variable effects. No behavioral effects were found at the lower dose levels. It is concluded that the behavioral perturbations produced by pulsed microwave irradiation were thermal in nature.