A retrospective rubella serological survey spanning a 14-year period (1973-1986) was carried out on 5,726 subjects (2,339 diseased patients and 3,387 healthy females) of various ages and mostly living in the town of Siena or in its surroundings. Rubella antibodies were assayed by a haemagglutination-inhibition technique. The infection rate, as inferred from the analysis of the seropositivity rate according to age, peaked in the 6 to 10 year age group and was apparently very low in subjects aged over 30. The overall seropositivity rate of healthy females of childbearing age was 88.4%. Notwithstanding the fact that rubella vaccination has been recommended for all school-girls since 1973, no significant difference was noticed between the seropositivity rates of healthy females aged 18-23 observed in the period 1973-78 (i.e. before the first immunized subjects reached this age group) and in the period 1981-86 (i.e. when this age group had already been included among the first vaccinees). Serological diagnosis of acute rubella infection was achieved in 44 (1.9%) of the 2,339 diseased patients. Most diagnoses occurred in spring months.