The original aim of this study was to characterise some aspects of the thermophysiology of a terrestrial vertebrate ectotherm which is physiologically adapted to tolerate and to be active over a wide range of body temperatures including low temperatures. The intention was to investigate the physiological performances of a eurythermic lizard over as wide a temperature range as was biologically and technically practicable and at different levels of organisation (organismal, organ and tissue). The small eurythermic skink Leiolopisma zelandica was chosen because of its abundance locally. Preliminary experiments indicated that certain physiological responses of the intact animal could be determined over the range -5° to 40° C. During the course of this investigation, information about the general biology and thermal relations of L. zelandica was also obtained, In addition, a large number of experiments were conducted at the temperature extremes of this species to explore physiological and behavioural responses to high and low temperatures. The bulk of the work on the thermophysiology of whole animals and tissues has been written up as two manuscripts in a style suitable for publication (Section 1, Papers A and B). A second section was erected to contain more thorough accounts of the biology, thermal relations and responses to temperature extremes of L. zelandica (Section 2, Parts A and B). Because most of the thermophysiological work was presented in the more concise format of a manuscript, it was necessary to elaborate in appendices on pertinent information regarding equipment and procedures. Data presented graphically in Papers A and B are tabulated in the final appendix. This approach to thesis presentation has necessitated some duplication of information within the thesis so that the Papers could be relatively autonomous. Since, at the time of thesis submission, Papers A and B have not been sent to editors, a compromise was made between the traditional form of a dissertation and the manuscript style. Consequently, a certain amount of redaction is anticipated.