1. A method of non-invasive determination of the concentration of at least one analyte in the blood of a mammal, comprising the steps of: (a) projecting near infrared radiation on a portion of the body of the mammal, said radiation including a plurality of wavelengths; (b) sensing the resulting radiation emitted from said portion of the body; (c) deriving from the sensed resulting radiation a first expression for the magnitude of said sensed radiation as a function of wavelength of the sensed radiation; (d) pretreating said first expression to minimize the influence of instrument offset and drift to obtain a second expression for the magnitude of said sensed radiation as a function of wavelength; and (e) performing multivariate analysis of said second expression to obtain a value for the concentration of said analyte.