A noninvasive and nonocclusive skin patch (Sudormed) was investigated for the systematic collection of drugs of abuse over a period of several days. First, the applicability and user friendliness were tested by volunteers. The permeability of the polyurethane dressing from the outside to the inside for an aqueous solution was shown by incubating the outside layer with Rhodamine B. No fluorescence could be detected in the cotton pad beneath. A single dose experiment using theophylline as a model compound showed that there was a delay in time before the substance could be determined in the pad. The drug content decreased with increasing time of patch application. When eight volunteers participating in a methadone treatment were monitored, the substitute drug could always be detected in the patch associated with a minor concentration of EDDP. Besides, in some of the patches investigated, indications for an abuse of cocaine and heroin were found. The so-called sweat patch appears to be a valuable tool in clinical and forensic toxicology, as it offers a longer and prospective surveillance period compared with blood and urine testing.