To characterize the normal values of histamine release from basophil leucocytes in cord blood after stimulation with both IgE-mediating and non-IgE-mediating secretagogues, a population of 1,684 newborn infants was studied using a microfiber-based method for detecting histamine release. A wide variation in anti-IgE and Concanavalin A-induced histamine release in the population was found. An increase in osmolarity in the release media selectively enhanced the maximal IgE-mediated histamine release, in addition to an increase in sensitivity in the dose response for anti-IgE and Concanavalin A. Both anti-IgE and Concanavalin A mediated histamine release were found to be significantly associated with the concentration of IgE in cord blood. Furthermore, an increased sensitivity to the IgE-mediated response and a close correlation between anti-IgE and Concanavalin A histamine release were found in the group of newborns with high IgE levels. Gestational age at birth and histamine release after stimulation with both IgE-mediating, and non-IgE mediating secretagogues were found to be significantly related, thus suggesting a continuing maturation of the human basophil leucocytes in the last weeks of gestation. Parental atopic disposition also affected basophil releasability in cord blood.