The use of the 3 - 5 micrometers (MWIR) spectral region for IR search and track (IRST) systems is sometimes dictated by operational and technological factors. In daytime, sun scatter from the background may cause the inherent target contrast in this band to be washed out or even reversed in polarity. This paper examines the effect of scattered sun radiation on target contrast for three types of sensor scenarios -- surface based, airborne, and space based. The analysis was carried out using the LOWTRAN 7 computer code. Critical angular relations between the sensor line-of-sight and the sun direction were identified and optimum spectral bands, based on target contrast considerations, are suggested for sensors employing InSb and PtSi detectors. A set of field measurements in a surface-based sensor scenario is presented to illustrate the sun scatter analysis.