THERE WAS A STATISTICALLY SIGNIFICANT RISE IN THE MEAN IQ SCORE OF CHILDREN WHOSE PARENTS OBTAINED THEIR LIVING BY FARMING IN MAHASKA COUNTY, IOWA, DURING THE TWENTY YEARS PRECEEDING 1961-63. HOWEVER, THIS INCREASE WAS NOT PARALLELED BY THE NONFARM CHILDREN LIVING WITHIN THE SAME RURAL COMMUNITY. SELECTIVE MIGRATION WAS SHOWN TO BE AN ACTIVE FACTOR IN THIS INCREASE, BUT NOT THE ONLY OR PERHAPS EVEN THE MOST IMPORTANT FACTOR INVOLVED. SOME FACTOR OR FACTORS OF ENVIRONMENT POSSESSED BY THE FARM CHILDREN AND A SEGMENT OF THE NONFARM POPULATION APPEARS TO PROMOTE THIS INTELLECTUAL GROWTH. (CL)