Abstract: The body chemistry of a person is determined by directing a beam of light into the eye of the person, measuring the spectral response of the eye to the beam of light, comparing the measured spectral response to a standard spectral response, and forming a conclusion as to the chemistry of the body from the comparison. The light selected for the measurement does not harm the eye, and is preferably in the ultraviolet or infrared ranges. The response of the eye chosen for measurement is that of reflected, fluoresced, or scattered light. It is preferred to use two or more of these techniques simultaneously, to minimize the likelihood of error. The comparison is made by comparing the measured response of the eye to a standard response from a library of previously established responses.