This paper reports the preliminary results of two years of herpetogeographic studies in the region called «Grande Porto Alegre» at its northern portion. The physiognomy shows, at North, slopes of the Brazilian Southern Plateau, more or less forested in a general view; these elevations graãuálly decrease to the South until the levei of the sea to Atlantic littoral by the eastern border, and to Rio Grande do Sul savanah, which extends to Uruguay and Argentina. The biota is transitional from the highland prairies and forests of the plateau to lowland prairies of the pampas. Three faunistic Provinces are included: Guarani, Pampean, and Tupi. The most conspicuous dispersion is shown by the taxa proceeding from the plateau to savanah (Dispersion Centre Guarani); the pampean species occur in low percentage (Dispersion Centre Uruguay), and an inappreciable account of Tupi fauna (Dispersion Centre of «Serra do Mar»). The new records are: presence of Chironius pyrrhopogon, Hydrodynastes gigas, Bothrops neuwiedi para-naensis, Micrurus corallinus; intergradation zone of Guarani and Pampean geographic roces; and new taxa of snakes, which will be described brieflly. The systematic composition presents: Chelonia, 4 (3 Chelidae, 1 Testudinidae); Sauria, 10 (1 Gekkonidae, 2 Iguanidae, 1 Anguidae, 3 Teiidae, 3 Amphisbaenidae); Serpentes, 45 (35 Colubridae, 4 Elapidae, 6 Viperidae); Crocodylia (1 Crocodylidae).