The expression of intermediate filaments (IMF) by K562 leukemic cell line has been studied by the use of polyclonal and monoclonal antibodies. These cells exhibited an extremely rich network of IMF reacting with both anti-vimentin and anti-keratin antibodies. Although these results need to be confirmed by different techniques, such as immunoblotting, they suggest the possibility that leukemic cell lines can express different types of IMF similarly to other cultured cells.