DO CHILDREN RAISED IN ENVIRONMENTS ASSOCIATED WITH LATER DEFICITS IN PSYCHOMETRIC INTELLIGENCE SHOW ANY DEFICITS DURING INFANCY AND, IF SO, WHEN DO SUCH DEFICITS APPEAR AND WHAT ABILITIES ARE AFFECTED. ARE THE ENVIRONMENTAL FACTORS ASSOCIATED WITH EARLY DEVELOPMENT OF INTELLIGENCE. FIFTY-ONE SLUM INFANTS AND A CONTROL GROUP OF 51 NON-SLUM INFANTS IN CHAMPAIGN-URBANA, ILLINOIS WERE TESTED IN THEIR 7TH, 11TH, 15TH, 18TH, AND 22ND MONTHS BY 3 SUB-SCALES OF THE INFANT PSYCHOLOGICAL DEVELOPMENT SCALE, AND 3 OTHER MEASURES OF DEVELOPMENT. IN ADDITION, EACH INFANT WAS HOME TESTED BY AN EXAMINER WHOSE NOTES WERE LATER TRANSLATED INTO A 4-POINT SCORING SYSTEM AND ADDED TO INFORMATION SUPPLIED BY THE INFANT'S MOTHER. DATA WERE ANALYZED USING THE SIGN TEST, AND THE RELATIONSHIP BETWEEN HOME STIMULATION AND DEVELOPMENTAL ITEMS WAS ANALYZED THROUGH POINT-BISERIAL CORRELATIONS. RESULTS INDICATED THAT SLUM INFANTS SHOW SLOWER DEVELOPMENT AT A MUCH EARLIER AGE THAN PREVIOUSLY SUSPECTED, SUGGESTING THAT COMPENSATORY PROGRAMS SHOULD START EARLIER THAN 3 YEARS OF AGE. IT ALSO APPEARS THAT, CONTRARY TO ACCEPTED HYPOTHESES, OVER-STIMULATION DURING INFANCY MAY BE MORE DETRIMENTAL THAN UNDER-STIMULATION AS AN ENVIRONMENTAL FACTOR. THIS PAPER WAS DELIVERED TO THE BIENNIAL MEETING OF THE SOCIETY FOR RESEARCH IN CHILD DEVELOPMENT IN NEW YORK, MARCH 29 - APRIL 1, 1967. (MS)