Suberythemal ultraviolet radiation (UVR) exposures of children are used routinely in Russia to prevent rickets and to strengthen general health. The aim of the present study was to re-evaluate the effects of such a regime on immune responses as UVR is now recognised to suppress cell-mediated immunity in many animal models. Seventeen infants were immunised with attenuated measles and recall polio vaccines of whom 10 had been given a course of prophylactic UV exposures before the vaccinations. All the infants in the study developed an acute infectious conjunctivitis one week prior to the vaccinations and were convalescent at the time of the vaccination. They were bled on the day of the vaccinations and at several times thereafter to assess leukocyte percentages and plasma cytokine levels. On the day of the vaccinations, an active immune response was apparent. The UV-exposed children differed from the unexposed children by having a smaller percentage of natural killer cells and a higher percentage of CD25-positive cells. In the days following the vaccinations, the UV-exposed infants had a lowered percentage of total lymphocytes with increased percentages of monocytes, eosinophils, neutrophils and HLA-DR-positive cells as well as higher concentrations of plasma IL-1beta and IL-10 compared with the unexposed infants. There were no local or systemic clinical reactions to the vaccines in the UV-group while a moderate rise in temperature of three children in the unexposed group occurred. Thus the UV irradiations modulated leukocyte percentages and plasma cytokine levels following the vaccinations, perhaps through the activation of a T helper 2-like response.