Experience of employing over 60 people in a field research capacity who had or were using drugs suggests the main advantage can be their shared experiences with the target group. This can improve their access to drug using groups and the rapport between worker and subject/client. Information gained in this way can be used to refine HIV prevention interventions. Careful recruitment and supervision help reduce the risk of relapse or evangelism. Drug user or ex-user workers should be treated on a par with their professional colleagues.