Our present understanding of breast cancer indicates that increased metabolic activity occurs and thus produces a local temperature increase. This paper evaluates present thermographic techniques used to detect these temperature increases and examines the problem of skin emissivity variations that can produce erroneous temperature measurements. These false temperature variations are on the order of the decision level used by radiologists, and therefore they can cause significant confusion in the interpretation of the thermogram. The ratio temperature thermograph is shown to reduce the effects of emissivity by measuring the spectral radiance at two prescribed wavelengths and ratioing the results. A dual-channel ratio thermo-graph was built using state-of-the-art detectors and electronics to prove its feasibility. The ratio temperature thermograph was quantitatively evaluated for small emissivity variations. This evaluation demonstrated the instrument's capability of minimizing emissivity effects. It was also evaluated for the detection of temperature changes.