1. The sensitivity of Type I slowly adapting mechanoreceptors in cat and monkey skin to temperature and changes in temperature was investigated.2. Multiple receptors innervated by a single axon appeared to be more frequent in the monkey than in the cat skin.3. The responses of these receptors to thermal stimulation at static skin temperatures from 27 to 40 degrees C were similar in cats and monkeys. At 43 degrees C the monkey receptors showed a higher steady-state activity than the cat receptors.4. A maximum steady-state frequency of 5.5 impulses/sec occurred in both the cat and monkey receptors at a static skin temperature of 37 degrees C.5. The maximum dynamic response to cooling occurred at a skin temperature of 40 degrees C. The response was near its maximum at 2 degrees C cooling and increased but little with further increases in the intensity of cooling.6. Dynamic responses to cooling disappeared after the skin had been heated to 51 degrees C for 35 sec and to mechanical stimulation after heating to 53 degrees C for 35 sec. Excitation by either mechanical or thermal stimulation did not reappear within 1-2 hr.7. The response characteristics of the Type I slowly adapting mechanoreceptors to temperature and temperature changes differ from those of specific cold receptors.