Eighty-one patients with non-Hodgkin's lymphoma had serum beta 2-microglobulin (beta 2M) estimated at presentation. A significant association was found between beta 2M levels and stage of disease (P less than 0.001), presence of hepatomegaly (P less than 0.001) and bone marrow involvement (P less than 0.05). No association was found between the level of beta 2M and histological group, presence of splenomegaly, lymph-node masses greater than 5 cm in diameter, lymphocyte count or the presence of systemic B symptoms. Pretreatment levels of beta 2M did not help predict response to treatment and achievement of a complete remission, the length of remission obtained or survival.