We recently characterized a novel putative intermediate-filament associated protein which is strongly expressed in the Reed-Sternberg cells of Hodgkin's disease. Therefore we named the protein‘restin’, an acronym forReed-Sternbergcell intermediate filament-associated protein. The protein is also expressed in anaplastic large cell lymphoma or Ki-1 lymphoma, a non-Hodgkin's lymphoma phenotypically related to Hodgkin's disease. Although the functions of restin are not yet fully elucidated, transfection experiments demonstrate that over-expression of the protein increases cell growth by a mechanism which may involve upregulation of the transferrin receptor. Hence, restin may contribute to neoplastic transformation in Hodgkin's disease and anaplastic large cell lymphoma. Study of the mechanisms leading to restin overexpression may provide important data on the etiology of Hodgkin's disease and its relation to anaplastic large cell lymphoma.