THIS STUDY INCLUDED ALL 56 PEOPLE CHARGED WITH HEROIN OFFENSES AND ALL 792 MARIJUANA DEFENDERS WHO WERE ARRAIGNED DURING 4 NONCONTINUOUS SAMPLE WEEKS DURING 1979. THE PROBATION CENTRAL FILE PROVIDED DATA REGARDING PRIOR CRIMINAL AND DELINQUENCY RECORDS OF THESE 848 DRUG DEFENDANTS. IT WAS FOUND THAT PERSONS CHARGED WITH DISTRIBUTING OR POSSESSING HEROIN WERE SUBSTANTIALLY OLDER THAN THOSE CHARGED WITH MARIJUANA OFFENSES. WHILE 63 PERCENT OF THE HEROIN DEFENDANTS WERE 26 OR OLDER, ONLY 16 PERCENT OF THOSE CHARGED WITH MARIJUANA OFFENSES WERE OVER 25. ONE OUT OF SEVEN HEROIN OFFENDERS WERE FIRST OFFENDERS, WHILE 2.6 OUT OF SEVEN MARIJUANA OFFENDERS WERE FIRST OFFENDERS. THE AVERAGE HEROIN DEFENDANT HAD PRIOR CONVICTIONS IN MORE THAN THREE DIFFERENT CATEGORIES OF CRIME, WHILE MARIJUANA DEFENDANTS HAD PRIOR CONVICTIONS IN LESS THAN TWO CATEGORIES. A GREATER PERCENTAGE OF HEROIN DEFENDANTS HAD PRIOR CONVICTIONS IN DRUG CRIMES, CRIMES AGAINST PERSONS AND PROPERTY, NONASSAULTIVE SEX CRIMES, MAJOR MOTOR VEHICLE OFFENSES, AND PUBLIC ORDER VIOLATIONS. FINALLY, NEARLY ONE-THIRD OF THE HEROIN OFFENDERS HAD PREVIOUSLY BEEN COMMITTED TO A CORRECTIONAL FACILITY AS COMPARED TO ONLY 1 OUT OF 12 MARIJUANA OFFENDERS. THE STUDY CONCLUDES THAT PEOPLE CHARGED WITH HEROIN-RELATED CRIMES SHOWED MORE SERIOUS PRIOR CRIMINAL BEHAVIOR THAN THOSE CHARGED WITH MARIJUANA OFFENSES. TABLES ARE INCLUDED. (AUTHOR ABSTRACT MODIFIED--) (JLF)