Results show that for chronic antisocial behavior measured by the respondent's number of police contacts, DAT1 is consistently predictive for the full sample, the White subsample, and the Black subsample. The effect has stronger statistical significance among Whites than Blacks. For all three models, the effects of DAT1 were conditioned by the friendship network within which an individual imbedded. 5HTT was related to chronic offending among African-American youths with low numbers of delinquent peers. The control variables were related to chronicity and dangerousness in the expected directions. Age was inversely related to both dimensions of career criminality; younger respondents tended to accumulate a greater frequency of police contacts, even for dangerous crimes. Males were significantly more likely than females to amass police contacts and engage in violent behavior; gender was a stronger biological correlate of career criminality than genetic polymorphisms. Data were collected from more than 90,000 students between the ages of 11- and 19-years-old beginning in 1994 from 132 middle and high schools. Tables and references