Chlorpropamide-alcohol flushing (CPAF) has been advanced and challenged as a specific marker for familial noninsulin dependent diabetes mellitus. The previous studies assay flushing reactions employing arbitrarily defined critical threshold values of rise and rate of rise in facial temperature. Since these methods ignore the curvilinear relationship between skin temperature and cutaneous blood flow, errors of analysis obtained, Further, the role of baseline facial temperature is obfuscated. The method of malar thermal circulation index derived from the relationship between skin temperature and cutaneous blood flow provides a more accurate assay method and permits the characterization of the role of baseline facial temperature. Baseline facial temperature is less in subjects with CPAF and noninsulin dependent diabetes than in normal subjects. The lower baseline facial temperature alone may account for the reported differences in the parameters of the CPAF test.