The antibiotic-resistance of 450 strains of Salmonella isolated by the Microbiology Unit of the hospital of Modena during the years 1975-1977 was examined. During the study, the following antibiotics were assayed: ampicillin, kanamycine, tetracycline, chloramphenicol, streptomycin, sulfonamides, trimethoprim, tobramycin, gentamicin and nalidixic acid. The transfer capacity of antibiotic-resistance was measured by the double conjugation of E. coli K-12. During the period studied, a remarkable reduction was noted in those strains with multiple resistance (3 or more elements) decreasing from 72.9% in 1975 to 23.5% in 1977. These phenomena are due to the decrease of the serum-type wien during the years under study. Antibiotic-resistance demonstrated itself most frequently to streptomycin and tetracycline; and chloramphenicol-resistance showed the highest transfer capacity (97.2%).