THE STUDY SUBJECTS INCLUDED FOUR GROUPS: (1) 35 TALL (AT LEAST 72 INCHES) MALES; (2) 12 TALL, YOUNG MURDERERS WHOSE OFFENSES HAD BEEN VIOLENT, SENSELESS, AND IMPULSIVE (PREPSYCHOTIC TYPES WITH HIGH FANTASY LEVELS); (3) 8 MENTALLY DEFICIENT MALES WITH INTELLIGENCE QUOTIENTS (IQ) BELOW 75; AND (4) 10 DOMINANT LESBIANS (PERSONS WHO WERE PHYSIOLOGICALLY FEMALE BUT PSYCHOLOGICALLY MASCULINE). THE SEX CHROMATIN PATTERN WAS OBTAINED FROM EPITHELIAL CELLS OF THE BUCCAL MUCOSA, WHILE THE KARYOTYPES WERE OBSERVED FROM BLOOD LEUKOCYTE CULTURES. ONE INMATE FROM THE FIRST GROUP HAD THE ABNORMAL 47,XYY CHROMOSOME PATTERN THOUGHT POSSIBLY TO BE ASSOCIATED WITH DEVIANT BEHAVIOR. ALL OTHER INMATES HAD NORMAL CHROMOSOME CONFIGURATIONS. THE ONE CHROMOSOMALLY ABNORMAL INMATE WAS NEITHER AGGRESSIVE NOR MENTALLY DEFICIENT. ASIDE FROM HIS HEIGHT, HE SHARED NO CHARACTERISTICS WITH THE MORE THAN 300 PERSONS REPORTED IN THE LITERATURE AS HAVING THE XYY KAROTYPE. A PHOTOGRAPH OF THE 47,XYY KARYOTYPE AND A LIST OF REFERENCES ARE INCLUDED.