Two commercially available yield monitors and one developmental model were field tested in Mississippi. This study was a component of an on-going research effort exploring within-field variability in crop yield and quality. The main objective of this study was to measure the accuracy and reliability of yield monitors for on-farm use. Yield monitor accuracy was reduced by dust build-up on the sensor face. Strands of cotton caught on imperfections in the picker chute also contributed to sensor inaccuracies. The continual drift observed in sensor accuracy together with the inability to distinguish between trash and lint limit the utility of currently available monitors in a production setting.