Five subspecific taxa belonging to the iguanid Phymaturus patagonicus have been reported in a previous paper (Cei and Castro, 1973). They correspond to different and isolated geographical districts of the extended patagonian range of the species, between 36° and 46° South Latitude. The northernmost form recognized was Phymaturus patagonicus payuniae, living in the basaltic rocks of the volcanic plateau of Payun, 2000 m, in southern Mendoza Province, near the Rio Grande and Colorado rivers. In late December 1973, a new form of the complex was discovered, 100 km northeast of the Payun plateau, on the southwestern slopes of the Sierra del Nevado range, the terminal volcanic relief, with many patagonian ecological features, facing the central Argentine lowlands. The form differs from all the recognized subspecies of Phymaturus patagonicus, especially from the neighboring Phymaturus patagonicus payuniae, by a number of significant morphological characters. It is described here as: Phymaturus patagonicus nevadoi subsp.n.