It has recently been reported that overexpression of leukemia inhibitory factor (LIF) in mice transgenic for LIF causes invagination of the anterior wall of Rathke's pouch leading to the formation of cysts lined by LIF immunoreactive epithelial cells. Strong immunoreactivity was also found in human Rathke's cleft cysts. Because such cysts and craniopharyngiomas share a common histogenesis, we raised the question of whether LIF is also expressed in craniopharyngioma.Fourteen histologically verified craniopharyngiomas of adamantinomatous type were examined for LIF immunoreactivity using the streptavidin-biotin-peroxidase complex method. Rabbit-anti-LIF antibody dilution 1:40) was applied to tissues having undergone antigen retrieval (microwaving in citrate buffer at pH 6). For positive control, nontumorous pituitary tissues were used. Primary antibody substituted with phosphate-buffered saline served as a negative control.By immunocytochemistry, the epithelial cells of all 14 craniopharyngiomas were LIF immunoreactive, showing varying degrees of staining intensity. In comparison, the connective tissue components of the tumors were immunonegative.Our study provides evidence that LIF is expressed in the epithelial cells of craniopharyngioma. Further investigation is required to elucidate the possible role of LIF in the development and progression of craniopharyngiomas.