For the Senate, 237 single-seat constituencies were established, even if the assembly had risen to 315 members. The candidates needed a landslide victory of two thirds of votes to be elected, a goal which could be reached only by the German minorities in South Tirol. All remained votes and seats were grouped in party lists and regional constituencies, where a D'Hondt method was used: inside the lists, candidates with the best percentages were elected.
The election was a test for the new organization of the socialist area, which was divided between the new revolutionary and Communist-allied Italian Socialist Party of Proletarian Unity and the governmental social-democratic federation between PSI and PSDI. The polls said that the split of the PSIUP in 1964 had not been a purely parliamentary operation, but the reflex of divisions into the leftist electorate. The result shocked the PSI's leadership, causing the sudden sinking of the social-democratic federation, and an alternance of provisional retirements by the government, firstly led by lifetime senatorGiovanni Leone and then, through two political crisis, by DC's secretary Mariano Rumor. Unsuccessfully trying to recover its lost leftist electors, the PSI returned to the alliance with the PCI for the regional elections of 1970, so causing another crisis and a new change of premiership, then led by Emilio Colombo, but the government coalition had continuous problems of instability. Influent Giulio Andreotti tried to resurrect the centrist formula in 1972, but he failed, opening the way to the first early election of the republican history.