RT Journal A1 WEISSMANN G, XEFTERIS ED T1 PHenylbutazone leukopenia JF A.M.A. Archives of Internal Medicine JO A.M.A. Archives of Internal Medicine YR 1959 FD June 1 VO 103 IS 6 SP 957 OP 961 DO 10.1001/archinte.1959.00270060109014 UL http://dx.doi.org/10.1001/archinte.1959.00270060109014 AB While effective in a variety of rheumatic conditions, phenylbutazone has incurred the reputation of being a relatively toxic drug. Purpura,1 depression of erythropoiesis,2 aggravation of bleeding ulcers,1 and Stevens-Johnson syndrome3 have been reported consequent to its administration, but by far the most alarming complications of phenylbutazone therapy have been agranulocytosis and, more frequently, leukopenia.1 The nature of white cell damage produce by this agent has not been previously elucidated, although structural similarities to aminopyrine have caused speculation as to analogous leukotoxicity.Certain drugs, when added to the serum of patients with leukopenia, will cause agglutination of autologous and homologous white blood cells. Gold and aminopyrine particularly have been mentioned in this regard.4 It is the purpose of this communication to add phenylbutazone to this list and to examine the relationship that the drug bears to aminopyrine in leukoagglutination activity. We have studied a patient whose serum caused agglutination of homologous