Substantial part of patients who suffer from food allergy outgrow their allergic reaction. Moreover the mechanisms of this phenomenon are poorly understood. We studied cytokine mRNA expression in peripheral blood mononuclear cells (PBMC) from children with egg allergy, nine patients on active stage and eight were outgrown, and four healthy controls, by use of reverse transcription polymerase chain reaction. Following ovalbumin (OVA) stimulation in vitro, active patients demonstrated increasing IL-5 mRNA. In comparison, no increasing expression of IL-5 mRNA was observed in outgrown and healthy children. IL-4 and IFN-gamma mRNA expression has no tendency either to increase or to decrease in all three groups. There was no difference of proliferative responses for OVA among these groups suggesting that outgrown patients' PBMC did not fall into anergy or clonal deletion. These data suggested the change in balance of cytokine production of PBMC which were stimulated by allergen is a trigger for "outgrow" of food allergy.