SummaryUrinary neopterin and biopterin concentrations were measured in 32 healthy controls and 53 patients with newly diagnosed haematological malignancies classified and staged by accepted criteria. The neopterin concentrations were only significantly raised in chronic lymphocytic leukaemia at stages III—IV. Total biopterin concentrations after oxidation with iodine at acid pH were decreased in chronic lymphocytic leukaemia stages O—II, multiple myeloma, and acute myeloid leukaemia but not in chronic lymphocytic leukaemia stages III—IV. Although of research interest, neopterin concentrations proved of little prognostic value at presentation, but taken with the biopterin concentration they may be useful for the assessment of tumour act