Identification of the hairy cells of leukaemic reticuloendotheliosis by an esterase method.

A distinctive pattern of alpha-naphthyl butyrate esterase positivity was observed in all of a series of 14 patients with HCL. This pattern was not observed in a range of other haematological malignancies including nine cases of CLL, two cases of Sézary's syndrome, six cases of null cell ALL, two cases of Schilling-type monocytic leukaemia and one case of lymphosarcoma cell leukaemia. The potential diagnostic value of this simple cytochemical test is discussed in relation to existing methods.