Research work was done to develop an automatic steering control system for an over-the-row apple harvester which has been built by the U. S. Department of Agriculture. A steering control system using noncontact sensors was designed for the apple harvester so that the harvester would automatically drive over a tree row. The sensing system consisted of several ultrasonic transducers that were used to measure the position of an apple tree trunk. This sensing system which is also called a sonar system was designed. Tests were done to determine the accuracy of the sonar measurements and the beam angle of the sonar transducer. The test results indicate that the accuracy of the sonar range measurements were affected by changes in the air temperature. Work is near completion for the development of a simulation model of the control system and for performance tests of the control system.