TO STUDY EFFECTS OF EARLY INTERVENTION ON CHILDREN, AN EXPERIMENTAL GROUP OF 13 SUBJECTS (AGED 7 TO 30 MONTHS, IQ 35 TO 89) WAS TRANSFERRED FROM AN ORPHANAGE TO THE INTENSE STIMULATION OF A MOTHER SURROGATE AT AN INSTITUTION FOR THE MENTALLY HANDICAPPED. A CONTRAST GROUP OF 12 SUBJECTS (AGED 11.9 TO 21.8 MONTHS, IQ 50 TO 103) REMAINED AT THE ORPHANAGE. TWO YEARS LATER, THOSE IN THE EXPERIMENTAL GROUP SCORED AN AVERAGE GAIN OF 28.5 IQ POINTS, AND THOSE IN THE CONTRAST GROUP SCORED AN AVERAGE LOSS OF 26.2 IQ POINTS. IN A FOLLOWUP STUDY 2 1/2 YEARS LATER, 11 EXPERIMENTAL GROUP CHILDREN WHO HAD BEEN PLACED IN ADOPTIVE HOMES HAD INCREASED THEIR GAINS IN INTELLIGENCE, BUT TWO EXPERIMENTAL GROUP CHILDREN NOT PLACED HAD DECLINED IN RATE OF MENTAL GROWTH. CONTRAST GROUP SUBJECTS HAD MADE SOME SLIGHT GAINS IN IQ BUT WERE STILL CONSIDERED MENTALLY RETARDED. AFTER 21 YEARS ALL CASES WERE LOCATED, AND THE TWO GROUPS HAD MAINTAINED THEIR DIFFERENCES. ALL 13 IN THE EXPERIMENTAL GROUP WERE SELF-SUPPORTING OR FUNCTIONING ADEQUATELY AS HOUSEWIVES. EDUCATIONAL AND OCCUPATIONAL ACHIEVEMENT AND INCOME COMPARED FAVORABLY WITH 1960 U.S. CENSUS FIGURES. OF THE CONTRAST GROUP, ONE HAD DIED IN A STATE INSTITUTION, ONE WAS IN A MENTAL HOSPITAL, THREE WERE IN INSTITUTIONS FOR THE MENTALLY RETARDED, AND THE REST WERE EMPLOYED. IN EDUCATIONAL ATTAINMENT, THE EXPERIMENTAL GROUP HAD COMPLETED A MEDIAN OF GRADE 12, BUT THE CONTRAST GROUP HAD A MEDIAN BELOW GRADE 3. THE CONTRAST GROUP HAD A SIGNIFICANTLY LOWER EDUCATIONAL LEVEL (.001 LEVEL, T TEST). ANALYSIS USING THE MEANS OF THE THE TWO GROUPS ON THE WARNER INDEX OF STATUS CHARACTERISTICS MEASURING OCCUPATIONAL STATUS REVEALED THE CONTRAST GROUP WAS SIGNIFICANTLY LOWER (.01 LEVEL, T TEST). THE COST TO IOWA FOR THE CONTRAST GROUP WAS APPROXIMATELY FIVE TIMES THAT OF THE COST OF THE EXPERIMENTAL GROUP, WITH ADDITIONAL COST TO THE STATE CONTINUING FOR THE FOUR INSTITUTIONALIZED SUBJECTS. TABLES AND SEVERAL CASE SUMMARIES ARE PRESENTED. A LIST OF 22 REFERENCES IS INCLUDED. THIS DOCUMENT IS VOLUME 31, NUMBER 3, OF MONOGRAPHS OF THE SOCIETY FOR RESEARCH IN CHILD DEVELOPMENT WHICH WAS PUBLISHED BY THE UNIVERSITY OF CHICAGO PRESS, CHICAGO, ILLINOIS 60637, AND IS PRICED AT $3.00. (JA)