To better characterize the cytokine response to measles virus vaccine, we examined the levels of IL-2, IL-4, IL-5, IL-10, IL-12 and gamma-interferon (gamma-IFN) in measles virus-stimulated peripheral blood mononuclear cells from 18 donors before and 2 weeks after vaccination. Donors were grouped as seropositive or seronegative on the basis of measles-specific IgM antibody present at 2 weeks postvaccination. After vaccination, similar levels of upregulation of IL-2 and gamma-IFN mRNA were observed in the two groups. The majority of donors in both groups did not exhibit an increase in measles specific IL-4 or IL-10 mRNA after vaccination. IL-12 mRNA was not induced by measles virus in any of the donors. A statistically significant upregulation of IL-5 mRNA was observed among seropositive (9/13) compared with seronegative (1/5) donors after vaccination (P=0.09, one tailed Fisher's test). The observed measles specific induction of IL-5 mRNA is suggestive of a possible association between IL-5 production and an antibody response to measles virus.