It may be advantageous to use sweat, rather than blood or urine, to monitor individuals' drug exposure for the purposes of drug treatment programs, employment initiatives, and forensic investigations. Forty-eight patients receiving methadone at the Public Service for the Treatment of Drug Dependence of Perugia (Italy) were monitored for 14 days by the analysis of methadone and cocaine present in two sweat patches, each worn for 7 days. The results were compared to those from the analysis of urine samples collected at the beginning of the study and after 7 days, as well as those from the analysis of hair collected on the fourteenth day. Sweat patch analysis was positive for methadone and its metabolite EDDP in 100% of patients. Some individuals were positive for cocaine in urine, sweat, and hair while others were positive for cocaine in only one of those samples. Results suggest analysis of a sweat patch indicates an individual's drug use or drug washout for the previous week, and provides an alternative to blood or urine analyses.