A new nematode, Pratylenehus steineri (Heteroderidae), that causes small pimples on the surface of potato tubers, is described. The disease is very similar to that incited by P. scribneri Steiner, 1943, in the United States. In the States, the disease was first studied by Scribner in 1889, who also determined its cause (1). Many years later, Steiner (4) published the description of the parasite. Pratylenehus steineri n. sp. closely resembles P. minyus Sher & Allen, 1953, from which it differs by its longer stylet, by the shape of its tail, and by some details in the organization of the ovary and lateral fields. P. steineri can be easily distinguished from P. scribneri by the more posterior position of the vulva. All developmental stages of the new parasite were found to occur in the potato lesions. The species seems to be monosexual since no males were found. A species of Helicotylenchus, not yet studied, was also obtained from the pimples. In addition, Eucephalobus sp., Ditylenchus sp., and another species of Pratylenchus were found associated with P. steineri in rare instances. In experimental potato fields belonging to the Instituto Agronômico de Campinas, Brazil, the percentage of tubers injured by the attack of P. steineri has ranged from 14.1 to 37.0 per cent in the last few years. The known area of distribution of the new species in the State of São Paulo, Brazil, is reported. Control measures are suggested that include crop rotation for 2 or 3 years, combined with selection of healthy seed.