The present investigation was carriied out in scald-shocked cats to observe the cardiovascular effects of diphenhydramine ( 2 mg/kg iv ) and cimetidine ( 20mg/kg iv ) . Changes in B-glucuronidase ( B-G ) activity and blood lactate level were also observed.lt was found that inanimals treated with cimetidine the cardiovascular parameter ( BP, LVSP , dP/dtmax, IP, VPm, HR ) were decreased significantly in 2 - 4 h after scalding. These results were the same as those of the saline-treated control. In animals treated with diphenhydramine, the cardiovascular parameters were increased in 1 h after administration of the drug and still persisted at normal level in 4h after scalding.There were no significant differences between groups in changes of B-G activity and the blood lactate level. These data suggest that the benefit of cimetidine in burn-shock is dubious and diphenhydramine may be of value as an adjuvant used in combination with other vasoactive drugs for the treatment of burn shock.