BACKGROUND & AIMS: Chronic intestinal lesions of patients with Crohn's disease (CD) are associated with a T helper (Th) 1-type cytokine profile, including high levels of interleukin 2 (IL-2) and interferon gamma (IFN-gamma). However, the mechanisms involved in the pathogenesis of the early mucosal lesions are poorly known. The aim of this study was to examine the pattern of Th1- and Th2-type (IL-4, IL-5, and IL-13) cytokines in the early ileal lesions occurring in patients with CD 3 months after ileal resection and ileocolonic anastomosis. Cytokines were also examined in the chronic ileal lesions to look for cytokine patterns related to disease progression. METHODS: Ileal biopsy specimens were obtained from 17 patients with CD and 11 controls. Mucosal IL-2, IFN-gamma, IL-4, IL-5, and IL-13 messenger RNA (mRNA) was evaluated by competitive reverse-transcription polymerase chain reaction. RESULTS: The early ileal lesions of patients with CD were associated with a significant increase of IL-4 mRNA and a decrease of IFN-gamma mRNA compared with the normal mucosa of patients with CD or controls. A Th1-type pattern was observed in the chronic ileal lesions. CONCLUSIONS: Divergent cytokine patterns are observed during different clinical stages of CD. These observations need to be considered in the development of newer specific therapeutic agents to prevent CD recurrences.