A sero-epidemiological survey was carried out on 555 serum samples from normal subjects of both sexes (age: from few months to over 60 years) collected in the late summer 1977 in Milan and Bari, two towns with rather different climatic conditions. In both localities a further large spread of A/Victoria/3/75 strain seems unlikely, since 54% of sera from Milan and 58% of those from Bari have h.i.a. at protective titers. On the contrary, the degree of immunity against B/Hong Kong/8/73 virus is still faiitical level for the survival of A/Hong Kong/68 pandemic strain appears almost reached in the population of Milan, where 76% of subjects have antibody at protective titers. In Bari such percentage is 60%. The statistical analysis (X2 test) of the data concerning the subjects with h.i.a. at titers greater than or equal to 1:40 shows only one significant difference between Milan and Bari, that is the A/Hong Kong/68 antibody prevalence. Probably this is due to the low number of males of Bari with protective antibody levels.