Devices and methods for non-invasively measuring at least one parameter of a sample, such as the presence or concentration of an analyte, in a body part wherein the temperature is controlled. The present invention measures light that is reflected, scattered, absorbed, or emitted by the sample from an average sampling depth, d.sub.av, that is confined within a temperature controlled region in the tissue. This average sampling depth is preferably less than 2 mm, and more preferably less than 1 mm. Confining the sampling depth into the tissue is achieved by appropriate selection of the separation between the source and the detector and the illumination wavelengths. In another aspect, the invention involves a method and apparatus for non-invasively measuring at least one parameter of a body part with temperature stepping. In another aspect, the invention involves a method and apparatus for non-invasively measuring at least one parameter of a body part with temperature modulation. In another aspect, the invention provides an improved method of measuring at least one parameter of a tissue sample comprising the steps of: (a) lowering the temperature of said tissue sample to a temperature that is lower than the normal physiological temperature of the body; and (b) determining at least one optical property of said tissue sample.