The effect of the administration of immune globulin (Ig), given during summer months to prevent hepatitis A, on the immune response to a simultaneously administered quadrivalent meningococcal polysaccharide vaccine (QMPV) was studied in Israeli military recruits. Data were obtained for the first time regarding the immune status of an Israeli population. Anticapsular polysaccharide antibodies were determined using a standardized ELISA assay before, 2 weeks and 3 months after QMPV immunization with or without Ig in two groups of recruits chosen to span the date determining seasonal administration or non-administration of Ig. Pre-vaccination antibody concentrations were > or = 2 microg/ml in 98.4 and 38.9% of subjects against serogroups A and C meningococci, respectively. These levels are consistent with the extremely low incidence of disease due to serogroup A in Israel, and with the previously documented occurrence of serogroup C disease in servicemen and women. Co-administration of Ig was associated with some reduction in antibody concentrations 3 months after vaccination, especially against serogroup A meningococci (P<0.05), but not to an extent likely to be of clinical significance.