Recent experiments in our laboratory have revealed a genetic correlation of the sensitivity of inbred mouse strains to different assays of nociception using noxious heat stimuli. An open question is whether the property of the noxious stimulus underlying the genetic correlation is heat specifically or simply a temperature (hot or cold) in the noxious range. The existing electrophysiological, psychophysical, neurochemical, and functional imaging literatures regarding the relationship of heat pain and cold pain are quite contentious, with a number of similarities and dissociations being documented. In the present study, we tested 12 inbred mouse strains (129/J, A/J, AKR/J, BALB/cJ, C3H/HeJ, C57BL/6J, C57BL/10J, C58/J, CBA/J, DBA/2J, RIIIS/J, and SM/J) for their reflexive withdrawal sensitivity to immersion of the tail in hot (47. 5 degrees C) and cold (-15 degrees C) water and compared the observed latencies with those obtained previously, using a 49 degrees C stimulus. All three traits displayed substantial heritabilities, ranging from 0.41 to 0.50. Strain means on these nociceptive traits displayed a high degree of cross-correlation (r = 0.49-0.77). Genetic correlation of hot and cold nociception implies that similar genes underlie interindividual variability in both traits in mice and further suggests that these nociceptive types share physiological mediation. This finding is discussed in relation to existing data in other mammals including humans.