The clinical symptoms of infestation with Trixacarus caviae in guinea-pigs are described. In general large areas of thickened, denuded skin, with a heavy secondary bacterial infection, and sometimes neurological signs, are observed in mangy cases. Antiparasitic therapy was successful with one or several washings with 0.15% trichlorphon or 0.07% lindane solutions. Histological examination of the skin of mangy guinea-pigs revealed acanthosis, pronounced thickening of the epidermis and increased indentations of the cutis. The mites were embedded in epidermal debris in the folds of the skin. They were often found in the superficial part of the hair follicles. Inflammation of the subcutis was pronounced. Healthy guinea-pigs developed mild signs of mange approximately 10 days after exposure by skin contact to heavily infested animals. These experimentally infested guinea-pigs recovered without treatment. An itching papular urticarial condition in three human patients was found associated with trixacariasis of guinea-pigs. The lesions were usually located on the skin areas in frequent contact with the infected animals. This human affliction cleared after terminating contact with the mangy pig or after antiparasitic treatment of the animal.