Data from a sample of 329 primary heroin users and from a sample of 301 regular amphetamine users were analysed in order to determine the extent and correlates of polydrug use among illicit drug users. Both samples exhibited high levels of polydrug use, with means of 5.2 (heroin) and 6.3 (amphetamines) drug classes used in the preceding 6 months. Multi-variate analyses indicated that being younger, being male, not being in treatment, being an injector, having recently borrowed injecting equipment and being from the regular amphetamine using sample were independently associated with higher levels of polydrug use. Rather than increasing levels of polydrug use being associated with age, illicit drug users appear to reduce their range of drugs as they get older. The 'pure' heroin or amphetamine user was extremely rare. It is concluded that to characterise drug users as 'heroin' or 'amphetamine' users misses the context in which these drugs are used.