BEFORE 1975, FCI-EL RENO WAS A MAXIMUM SECURITY FACILITY FOR YOUNG MALES WITH AN AGE RANGE OF 18 TO 26. IT BECAME A TRAINING GROUND FOR A PRIMITIVE TYPE OF SOCIALIZATION AND VIOLENCE WAS THE NORM. FCI-TEXARKANA WAS A MEDIUM SECURITY INSTITUTION WITH 90 PERCENT OF THE POPULATION OVER THE AGE OF 28 AND A RELATIVELY LOW LEVEL OF VIOLENCE. BASELINE DATA WAS COLLECTED FOR A YEAR BEFORE JULY 1, 1975. THEN THREE STRATEGIES WERE USED TO MAKE THE AGE COMPOSITION AT THE TWO FACILITIES MORE HETEROGENEOUS. IN LATE 1975, INMATES WERE REASSIGNED BETWEEN THE TWO INSTITUTIONS ON A RANDOMIZED BASIS WITH THE MAJOR CRITERION BEING INMATE AGE. AFTER THIS INITIAL EXCHANGE, DIRECT COURT COMMITMENTS WERE ASSIGNED TO THE TWO INSTITUTIONS ON THE BASIS OF AGE AND ROUTINE TRANSFERS FROM MAXIMUM TO MEDIUM SECURITY FACILITIES WERE AGAIN MADE TO ONE OF THESE INSTITUTIONS ON THE BASIS OF AGE. BEFORE THE EXPERIMENT BEGAN, ALMOST NONE OF THE EL RENO INMATES WERE AGE 28; BY FEBRUARY 1977, 36 PERCENT WERE 28 OR OLDER. THE PERCENTAGES OF INMATES UNDER AGE 28 AT TEXARKANA INCREASED FROM 10 TO 42 PERCENT. THIS CHANGE IN AGE MIX LED TO A SIGNIFICANT DECREASE IN VIOLENCE AT EL RENO (FROM 6.33 INCIDENTS PER 1000 INMATES TO 2.00). VIOLENCE AT TEXARKANA ROSE FROM .33 TO 1.17. INTERVIEWS WITH STAFF AND INMATES ALSO FOUND THAT THE ATMOSPHERE AT EL RENO HAD IMPROVED GREATLY, AND THAT OLDER INMATES HAD STABILIZED THE SITUATION. THE STUDY CONTAINS CHARTS, STATISTICS, AND REFERENCES.