The patch consists of a cellulose fiber absortion pad which is covered and held to the skin by adhesive. The patch allows for the normal exchange of water, oxygen, and carbon dioxide to the skin through the patch. At the same time, the patch resists water and environmental contaminants from the outside. The absorption pad collects and contains various components of sweat which do not evaporate, such as salts, proteins, and the parent drug and analytes from consumed drugs present in perspiration. The patch is easy to apply to skin and can be worn for only a few days or for as many as 14 days. In 1992, product evaluation studies of the sweat patch were initiated in California to evaluate its usability, wearability, practicality, and acceptability in the real life environment. Patch placement on the skin was designated by participants: lower chest along the lower rib cage, lower back above the belt line, or outside the upper arm. About 10 percent of 127 study participants were analyzed for the presence of five drugs (cocaine, opiates, amphetamines, marijuana, or phenylcyclidine). The sweat patch proved to have distinct advantages in drug testing and was conclusively preferred by offenders over urinalysis. Because the patch provided continuous monitoring, it significantly improved the management of subjects in a closely supervised drug testing program. Physiological aspects of the role of perspiration in eliminating waste products from the body are discussed. 17 references, 1 table, and 1 figure