A model MMC-4000, microwave-based technology, bale moisture sensor, manufactured by MALCAM Limited of Tel-Aviv, Israel, was evaluated in two gins in the South in 1996. The MMC-4000 responded directly to differences in moisture content in bales of cotton. At one gin most differences occurred between ±0.4%; at the other gin, the MMC-4000 indicated moisture levels at about 0.5% higher than oven moistures. In addition to moisture, the instrument responded strongly to temperature of the cotton as measured immediately before the tramper and to bale weight. Future research should address the impact of temperature and bale weight on moisture readings by the MMC-4000.