DATA ON AGGRESSIVE BEHAVIOR OCCURRING IN DADE COUNTY, FLA., WERE GATHERED FROM POLICE FILES ON AGGRAVATED ASSAULT OVER A 5-YEAR PERIOD (1969-1973), MEDICAL EXAMINER RECORDS ON SUICIDES AND FATAL TRAFFIC ACCIDENTS FROM 1956 THROUGH 1968, AND HOSPITAL RECORDS (AUGUST 1969 TO JUNE 1974) ON PERSONS WHO CAME TO THE EMERGENCY ROOM AND WERE SUBSEQUENTLY REFERRED TO A PSYCHIATRIST. COMPUTER ANALYSIS WAS USED TO EXAMINE THESE DATA IN CONNECTION WITH MOON PHASES. ALL FIVE CATEGORIES OF DATA SHOW LUNAR PERIODICITIES. HOMICIDE AND AGGRAVATED ASSAULT CASES CLUSTER AROUND FULL MOONS. PSYCHIATRIC EMERGENCY ROOM VISITS CLUSTER AROUND FIRST-QUARTER MOONS AND DECREASE SIGNIFICANTLY AROUND NEW AND FULL MOONS. THE SUICIDE CURVE CORRELATES WITH BOTH AGGRAVATED ASSAULT AND FATAL TRAFFIC ACCIDENTS, SUGGESTING A SELF-DESTRUCTIVE COMPONENT FOR EACH OF THESE BEHAVIORS. THE POSSIBILITY THAT THERE EXISTS A BIOLOGICAL RHYTHM OF HUMAN AGGRESSION THAT RESONATES WITH THE LUNAR CYCLE IS RAISED. SUPPORTNG DATA AND A LIST OF REFERENCES ARE INCLUDED. (AUTHOR ABSTRACT MODIFIED-LKM).