THE PROBLEM OF THIS RESEARCH WAS TO DEVISE A NEW, NONVERBAL AND NONLANGUAGE PROCEDURE FOR TESTING THE HEARING OF MENTALLY RETARDED CHILDREN IN WHICH IMPAIRMENT IN DISCRIMINATING PURE TONES AT THRESHOLD LEVELS WOULD NOT BE CONFUSED WITH IMPAIRMENT OF AUDITORY SENSITIVITY. OPERANT CONDITIONING TECHNIQUES WERE APPLIED TO TRAINABLE MENTALLY RETARDED, NORMAL, AND PHYSICALLY HANDICAPPED CHILDREN IN THE MEASUREMENT OF PURE TONE HEARING THRESHOLDS. RESULTS WERE COMPARED WITH THE THRESHOLDS OBTAINED PREVIOUSLY BY AUDIOMETRISTS EXPERIENCED IN EXAMINING EXCEPTIONAL CHILDREN WITH CONVENTIONAL METHODS. A PANEL EQUIPPED WITH LEVERS WAS USED WHICH, WHEN OPERATED UPON SOUND, DISPENSED REINFORCERS. WHEN THE SUBJECT PUSHED A SPECIFIC LEVER, REINFORCERS APPEARED AND SOUND DISCONTINUED. SOUND CAME FROM EARPHONES OR LOUDSPEAKERS AND WAS CONTROLLED BY AN OBSERVING OPERATOR. THE OPERANT CONDITIONING PROCEDURE PROVIDED VALID AND RELIABLE MEASUREMENTS OF HEARING THRESHOLDS IN THE MENTALLY RETARDED CHILDREN. THE RESULTS OBTAINED, AFTER EXPERIMENTATION WITH 67 CHILDREN SUPPORTED THE BELIEF THAT THE PROCEDURE WAS AN EFFECTIVE ONE. RECOMMENDATIONS FOR MORE STUDY WERE SUGGESTED. (GC)