The results of a multi-parameter analysis of opiates in the hair of drug users and victims of fatal poisonings with these xenobiotics have been presented. The analysis was carried out with the use of liquid chromatography coupled with mass spectrometry (LC-MS). The article discusses the monitoring of the drug users' adherence to pharmacotherapy and the usefulness of hair analysis for medico-legal purposes. The authors evaluate the differences in the contents of particular opiates in the hair as related to the origin of a sample (untreated drug user, drug user in the course of treatment, victim of fatal poisoning). The report presents differences between the Polish and American profiles of abuse, providing confirmation that a great part of drug users undergoing methadone treatment do not abstain from opiates and/or amphetamine, the latter as a rule being very often taken with opiates.