Subjects for the study came from a larger investigation of males who had been in a program designed to prevent delinquency. At the time of their introduction to the prevention program, the boys ranged in age from five to thirteen. Although the treatment program failed to better the lives of its charges, it left a legacy of carefully documented case materials that are used here to examine interacting effects of biological and environmental conditions that appear to promote or retard transmission of aggressive antisocial behavior. The evidence suggests that aggressive models promote criminality and that maternal behavior can reduce the probability that a son will imitate a criminal father. 8 tables and 25 footnotes (Publisher abstract)