Urine specimens from methadone treatment clinics were screened for various abused drugs between 1974-1979 by thin-layer chromatography (TLC) and immunoassay techniques (IAT). A comparison of the relative incidence of drugs abused reveals that IAT are more sensitive and detect far greater number of subjects abusing drugs than TLC. The results also show a significant abuse of heroin and cocaine during the period studied and a variation of the incidence of other drugs used during the same period. While these patients did not receive benzodiazepenes and tricyclic antidepressants by prescription, their abuse alone and in combination with each other was also found to be widespread. Low levels of PCP and/or its analogs were found in 1978 and 1979. The frequent finding of low levels of PCP in combination with other drugs indicates the availability of this hallucinogen and point to its use in combination with other illicit drugs such as cocaine, amphetamine, and heroin. The suggestion is made that more sensitive analytical methods for drug screening be utilized in methadone monitoring programs, and that other classes of drugs be added than are currently required.