Nonspecific esterase activity in 'hairy cells'.

Nonspecific esterase activity using alpha-naphthyl butyrate as substrate was found to be present in hairy cells from patients with hairy cell leukemia. Activity of this enzyme was markedly diminished and in some instances obliterated by sodium fluoride. Since alpha-naphthyl butyrate is believed to be a more specific substrate for monocytic-type nonspecific esterase than alpha-naphthyl acetate, its presence in hairy cells combined with fluoride inhibition which is also characteristic of monocytic nonspecific esterase provides additional evidence of monocytic properties of hairy cells.