Cytokines play an important role in the immune response to live measles virus immunization. To gain further insight into the cytokine production profile in response to measles vaccination, we studied interferon-gamma (IFN-gamma), tumor necrosis factor (TNF-alpha), soluble IL-2 receptor (sIL-2R), interleukin-2 (IL-2), interleukin-4 (IL-4), and interleukin-6 (IL-6) in both supernatants from peripheral blood mononuclear cells (PBMC) stimulated with phytohaemagglutinin (PHA), and plasma. We enrolled 57 healthy infants and children residing in an area where no measles virus circulated in their lifetimes. Overall analysis of cytokines in supernatants from PBMC showed that a predominant Th1 cytokine pattern occurs after the second dose of measles immunization. However, plasma levels of Th1 cytokines (IFN-gamma, sIL-2R and TNF-alpha) were preferentially activated by measles virus after the first dose of measles vaccination. Median IFN-gamma plasma levels were 1.73 pg/ml for infants compared to 0.63 pg/ml for older children (P = 0.003). These data suggest that after the first and the second dose of measles virus immunization, there is a predominant Th1-type directed immune response, but the Th1 cytokine pattern seems to be stronger in previously unvaccinated children. There was no correlation between cytokine production by PBMC supernatants after PHA stimulation and circulating levels of plasma cytokines. No relationship was found between any specific cytokine level and measles antibody level.