British public policy has in recent years been increasingly concerned with the prevention of heroin and cocaine use among young people, and specifically with steering people away from more damaging forms of drug use, such as injecting. This study investigated young cannabis users, who had never used heroin or injected it attending further education colleges across London of which 35 percent were found to have been offered heroin, 36 percent had been present during heroin smoking, and 12 percent were present at injecting. The study investigated factors associated with these exposure opportunities. The most striking initial finding was the extent to which this sample of young cannabis users had clearly been in situations in which harder drugs were being used. Both the subject’s own drug use and socio-demographic variables were predictive of the extent of involvement of friends in illicit drug use other than cannabis. Additional results and findings are presented and discussed. References