THE STUDY WAS CARRIED OUT AT A CALIFORNIA FACILITY FOR MENTALLY DISORDERED OFFENDERS. THE SUBJECTS COMPLETED THE BUSS-DURKEE HOSTILITY INVENTORY, THE MEGARGEE OVERCONTROLLED HOSTILITY SCALE, AND THE MICHIGAN ALCOHOLISM SCREENING TEST. THE RAPISTS WERE CLASSIFIED ACCORDING TO THE DEGREE OF VIOLENCE ASSOCIATED WITH THEIR OFFENSES. THE RANGES AND MEANS OF THE PLASMA TESTOSTERONE LEVEL FOR BOTH RAPISTS AND CHILD MOLESTERS WERE WITHIN NORMAL LIMITS. THE GROUP OF RAPISTS WHO WERE JUDGED TO BE MOST VIOLENT HAD A SIGNIFICANTLY HIGHER MEAN PLASMA TESTOSTERONE LEVEL THAN NORMALS, CHILD MOLESTERS, AND OTHER RAPISTS IN THE STUDY. THE HIGHEST TESTOSTERONE LEVEL WAS FOUND IN THE ONLY RAPIST WHO MURDERED HIS VICTIM. ALCOHOLIC RAPISTS HAD A SIGNIFICANTLY HIGHER MEAN PLASMA TESTOSTERONE LEVEL THAN NONALCOHOLIC RAPISTS. THE MEAN BUSS-DURKEE HOSTILITY SCORE FOR RAPISTS WAS SIGNIFICANTLY HIGHER THAN THE NORM, BUT THERE WAS NO CORRELATION BETWEEN INDIVIDUAL HOSTILITY SCORES AND TESTOSTERONE LEVELS. NOR WAS THERE A CORRELATION BETWEEN TESTOSTERONE LEVELS AND AGE, RACE, OR LENGTH OF INCARCERATION. THE FINDINGS SUGGEST THAT AGGRESSIVE RAPE PROBABLY IS NOT DETERMINED LARGELY BY HIGH LEVELS OF TESTOSTERONE. IN LIGHT OF EVIDENCE THAT ALCOHOL AFFECTS PLASMA TESTOSTERONE LEVELS, THE FINDINGS ALSO BEAR UPON THE ASSOCIATION BETWEEN AGGRESSION AND DRINKING. SUPPORTING DATA AND A LIST OF REFERENCES ARE INCLUDED. (LKM)