Two HPLC methods for histamine determination are recommended. Urinary histamine can best be determined using a concentration/cleanup technique with postcolumn derivatization with o-phthaldehyde (OPA). Plasma histamine, because of low natural occurrence and limited sample, is best determined by a precolumn derivatization with OPA. A brief description of technique and chromatograms are presented. Lower limits of detection for both methods are in the picogram range.