Replies to the article 'Serum thrombopoietin levels in acute leukemia patients with chemotherapy-induced cytopenia--inverse correlation between serum levels and platelet counts,' by &Empty Bruserud and B. Foss published in the October 1998 issue of the journal 'Leukemia.' Possible effect of the acute phase reaction on the serum levels; Regulation of the serum levels by several mechanisms.