S UBCUTANEOUS injections of an alum-precipitated pyridine extract of Rhus toxicodendron for prophylaxis of poison ivy dermatitis was first described by Strauss and Spain in 1946.l Many subsequent reports2V6 have confirmed its clinical usefulness. The series of relatively few painless injections produces only small local reactions, and is nonsensitizing. A unique opportunity was afforded this investigator to make a clinical evaluation of the alum-precipitated pyridine Rhus toxicodendron extract for the prophylaxis of poison ivy dermatitis in a group of 20 men who were employed daily in jobs of tree trimming, tree removal, and the installation of maintenance of gas and electric service in areas heavily infested with poison ivy. These men were thus directly exposed to the poison ivy plant or roots 5 days a week in contrast to the occasional exposure experienced by persons o,therwise employed. Although they had used general protective measures, such as showering with hot soapy water, frequent washing of their hands, rinsing with solvents, and wearing of gloves, each year these measures were found to be relatively ineffective and of limited value. In searching for another and more efficient method of protection, it was decided to use prophylactic treatments of the alum-precipitated pyridine extract of Rhus toxicodendron. The following clinical data represents two individual studies made in two consecutive years.