Abstract: Effect of two histamine receptor antagonists, chlorphenamine maleate and cimetidine, on pulmonary hypertension (PH) induced by low ambient temperature in broiler chickens were investigated. One hundred and forty 17-day broiler chickens were randomly divided into four groups.(1) normal temperature group(NT): forty birds were reared at 22 ~23 ℃ and normal saline was given twice by intramuscular injection each day.(2)Low ambitent temperature group(LT) : forty birds were reared at 9~11 ℃ and normal saline was given twice by intramuscular injection each day.(3)Chlorphenamine maleate group in low ambient temperature (CMLT): forty birds were reared at 9~11 ℃ and chlorphenamine maleate was given twice by intramuscular injection each day.(4)Cimetidine group in low ambient temperature (CLT):twenty birds were reared at 9~11 ℃ and cimetidine was given twice each day by intramuscular injection from 24 to 38 days of age. At 24, 31, 38, 45 days of age， 10 birds were randomly taken from each group except CLT.At 31, 38 days of age，10 birds were randomly taken from CLT. The following three parameters were measured : the pulmonary artery pressure (PAP) by right cardiac catheter，the ascites heart index(AHI) and the packed cell volume (PCV).The results were as follows:(1)At 24， 31, 38 days of age， the pulmonary artery systolic pressure and diastolic pressure of LT were significantly higher than that of NT (P＜0.05 or P＜0.01). The pulmonary artery systolic pressure of CMLT was significantly lower than that of LT at 24 days of age (P＜0.05). The pulmonary artery systolic pressure and diastolic pressure of CLT were significantly lower than that of LT at 38 days of age (P＜0.01). (2) The PCV of LT was significantly greater than that of NT ( P＜0.01) at 24， 31, 38, 45 days of age.At 24 days of age， the PCV of CMLT was significantly lower than that of LT (P＜0.05). At 31 days of age， the PCV of CMLT was significantly higher than that of LT (P＜0.01).(3) The AHI of LT was significantly greater than that of NT (P＜0.05) at 45 days of age.The AHI of CMLT was significantly less than that of LT (P＜0.05) at 45 days of age. The PAP was decreased at the early stage of treatment with chlorphenamine maleate, and was decreased at the late stage of treatment with cimetidine.These results indicated that histamine promote the development of PH induced by low ambient temperature in broiler chickens. The PAP was decreased at the different stage of treatment with two histamine receptor antagonists， so right ventricular hypertrophy was inhibited.