Neurofibromatosis type 2 (NF2) gene encodes a novel 595 amino acid protein named merlin. Recently, Ruttledge et al demonstrated inactivation of NF2 gene in approximately 60% of sporadically occurring meningiomas. Merlin is thought to physiologically exist beneath the cell membrane, and to form a part of modulation in signal transduction, for example, information concerning contact inhibition. In NF2-related tumors, it is supposed that the mutation of merlin results in loss of this signal transduction leading to tumorigenesis. In this paper, we investigated the expression of NF2 gene product merlin in arachnoid villi and meningiomas. The immunohistochemical staining of merlin showed a striking contrast between arachnoid villi and meningiomas. In arachnoid cells, merlin was labeled in the whole cytoplasm, but not within the nuclei. In contrast, in meningiomas, immunoreactivity of merlin was mainly seen in the nuclei. These results suggest that arachnoid cells with normal merlin are capable of normal signal transduction, whereas meningioma cells with mutated merlin show impairment of signal transduction which may lead to tumorigenesis.