ABSTRACT AN automatic feedback-control system was developed to adjust the combine threshing-cylinder speed bas-ed on a continuous-flow measurement of soybean moisture. Data are presented on the results of laboratory tests of the moisture sensor and the complete control system. Data are presented on variations in soybean moisture content caused by both time of day and soybean location in the field. Moisture-content variations were influenced more by different harvest times than by different posi-tions within the field. The moisture-sensor accuracy was affected by changes in the mass flow rate of grain. Control-system stability was dependent on speed of the adjustment motor.