Results are presented on replicated experimental plantings with ten Irish potatoes varieties in six localities of the State of São Paulo. These plantings were made to study yield, earliness, disease and pest resistance and also the mineral composition of each variety in the different localities. The varieties used were Alpha, Bintje, Doré, Eersteling, Eigenheimer, Geelblon, Libertas, Saskia, Voran and Z.P.C. - 40405. Under the conditions of the experiments the varieties Alpha and Voran were found to be somewhat resistant to Phytophthora blight; the varieties Eersteling, Saskia and Doré, were very susceptible. The Doré variety was susceptible to hollow heart, Eigenheimer and Bintje revealed a tendency of producing second growth tubers. Eigenheimer and Alpha had a higher percentage of tubers with spotted pulp. Saskia proved to be less affected by common scab, rhizoctoniosis and root-knot nematodes. Geelblon was very susceptibe to spindle tuber. Libertas, Alpha and Voran were late maturing varieties while Eersteling, Doré, Saskia and Geelblon were early maturing in these tests. Bintje and Eigenheimer had the highest yields followed by Voran, Doré, and the Alpha. The results of the chemical analysis revealed that the tuber skin has a higher water content and is richer in magnesium, calcium, and potassium than the flesh. Phosphorus is found in equal amounts in the skin and flesh. The content of the above-mentioned chemical elements was not significantly different in the studied varieties.