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Twelve mature, experimentally naive rats, all female albinos, were randomly but equally assorted into four groups and then were subjected to classical conditioning procedures in which the conditional stimulus (CS) was a 525-Hz auditory signal. A 30-s CS was presented during all phases of the study (habituation, 30 trials; conditioning, 200 trials; and extinction, 100 trials) to a Tone-Only control group. For rats of the three experimental groups, the CS antedated by 30 s and then continued until cessation of the unconditional stimulus (US) during the conditioning phase. For Tail-Shock rats, the US was a 2-s application of 60-Hz ac to the tail at 300 V rms; for the 10-s Microwave rats, 2450-MHz sinusoidally modulated irradiation that resulted in a dose rate of 420 mW g−1 was presented for ten seconds; and for the 30-s Microwave rats, irradiation that resulted in a dose rate of 220 mW g−1 was presented for 30 seconds. All three USs resulted in mean increments of colonie temperature (ΔTs¯) approximating 1.5°C. During habituation and extinction phases,the CS was presented without the US to all animals. A conditional response (CR or “learned” hyperthermia) of a modest sort was reliably demonstrated, was found to be highly resistant to extinction, but was also found to be a generalized reaction to the conditioning environment—although selective eliciting of CRs occurred outside the laboratory in the presence of the individual who trained the animals. The mean increments of conditionally elicited temperature were +0.37°C(2-s Tail Shock), +0.5°C (30-s Microwave), and +0.7°C (10-s Microwave), but while none of these ΔTs¯ differed reliably from each other, they all departed significantly from the negative ΔTs¯ of Tone-Only controls (−0.47)°C. Hyperthermia, whether calorically induced by microwaves or the endogenous product of an external trigger, appears to be “learnable” and could be a source of experimental confounding of any thermally sensitive assay in which noxious stimuli are repeatedly presented to the psychologically intact organism.