Two causes of nonlinearity are identified in cryogenic radiometric and interferometer systems: (1) multiple time constant response in doped germanium and silicon detectors, and (2) voltage sensitive thick-film resistors used as detector load or transirnpedance feedback resistors. Experimental methods used to evaluated the nonlinear coefficients include the variable source temperature method and the precision aperture method. The effects of nonlinear response upon radiometric systems is minimal: The multiple time con-stant effect results in an "S" shaped response curve as the detector responsivity varies with average signal. The voltage sensitive resistor effect causes a full-scale (10 V) nonlinearity of from 20 to 80%. The effect of nonlinear response upon the performance of an interferometer system results in the generation of false spectral. The linearity data are analyzed using least squares solution so the sensor precision can be determined over the range of measured values. The variable temperature method yields an rms error of about ±10% while the precision aperture method yields an rms error of about ±4% over 4 to 5 orders provided multiple data sets are used to extend the dynamic range of the apertures and to eliminate area dependent data.