119 specimens of blood sera collected from measles cases with different vaccination history (aged 4 months to 48 years) on 5th-6th days after rash onset were Investigated using EIA. The obtained results showed that the primary immune response (PIR) was developed in 59 patients; the secondary immune response (SIR) was developed in 60 patients with a significant increase in the specific high avidity IgG (22.34 IU/ml +/- 3.2). The specific IgM were detected in 100% cases studied with capture ELISA in both previously vaccinated and unvaccinated individuals of different age. The specific IgM were detected by indirect ELISA in 100% cases in unvaccinated patients, while IgM positive sera was defined only in 23.3% of individuals with SIR. It was concluded that measles virus infection in previously vaccinated and unvaccinated adults had clinical differences. The role of patients with SIR in virus transmission was discussed.