THE STUDY INVESTIGATED SOME OF THE RELATIONSHIPS BETWEEN A CHILD'S VERBAL BEHAVIOR AND ENVIRONMENTAL EVENTS NECESSARY IN ACQUIRING LANGUAGE. TWO TRAINABLE RETARDATES (FROM A GROUP OF SIX, AGED 3-6 TO 5) WITH A FUNCTIONAL VOCABULARY OF NO MORE THAN TWO OR THREE WORDS WERE SEEN INDIVIDUALLY IN 20- TO 30-MINUTE SESSIONS TWICE A WEEK DURING A 4-MONTH PERIOD. DURING MOST SESSIONS THE SUBJECTS HAD ACCESS TO SIX WOODEN BLOCKS, A PAD OR PAPER, A CRAYON, AND A PACKET OF 4 X 6 CARDS. THE EXPERIMENTER WAS USUALLY SEATED AT A TABLE. PROCEDURES VARIED WITH EACH CHILD, BUT ALL WERE CRUDE CONTINGENCY-MANAGEMENT PROCEDURES. THE MAJOR DEPENDENT VARIABLE WAS THE FREQUENCY OF VOICED VOCALIZATIONS BY THE TWO SUBJECTS. ECHOING VOICED VOCABLIZATIONS RESULTED IN AN INCREASE IN THE FREQUENCY OF VOCALIZATIONS. EYE FIXATION BETWEEN THE SUBJECT AND THE EXPERIMENTER INCREASED WHEN POSITIVELY REINFORCED (CHANGING FACIAL EXPRESSION OR WAVING THE HAND). ONE SUBJECT LEARNED TO RESPOND TO THE COMMAND "T----COME." THE OTHER SUBJECT PERFORMED A COLOR DISCRIMINATION TASK. DATA INTERPRETATION WAS DIFFICULT DUE TO WEAKNESS IN PROCEDURES FOR MEASUREMENT OF THE DEPENDENT VARIABLES. SESSIONS ARE RELATED, AND THREE FIGURES PROVIDE DESCRIPTIVE GRAPHS. SEVEN REFERENCES ARE CITED. (AA/JD)