Studies were made on the preference responses and tolerances of the troglobitic carabid beetle Rhadine subterranea to light, temperature, and relative humidity. The beetles are weakly photonegative and appear to have a strong preference for atmospheres of low saturation deficit. Both these responses seem to be orthokineses. They have a strongly developed temperature sense, and their temperature preferendum shifts seasonally. This response seems to be a klinotaxis. They are neither strongly stenothermal nor stenohygrobic. The preference responses, especially that of temperature, are probably mechanisms tending to restrict the beetles to their habitat. The tolerance data suggest that the epigeum could, at times, be used as a dispersal route.