In vitro activity: Xylazine dose-dependently inhibits norepinephrine release and lipolysis in beagle dogs. Xylazine also tends to decrease epinephrine levels dose-dependently. Xylazine hydrochloride dose- and time-dependently reduces amount of minimum alveolar concentration (MAC) in horse. Xylazine hydrochloride dose- and time-dependently increases blood glucose concentration in horse. Xylazine induces variable bilateral caudal analgesia extending from coccyx to S3, with minimal sedation, ataxia, and cardiovascular and respiratory depression in standing mares. Xylazine significantly decreases heart and respiratory rates, systolic, diastolic, and mean arterial blood pressure, PCV, hemoglobin concentration, arterial oxygen content, and oxygen transport. Xylazine results in significantly decreased heart rate, increased incidence of atrioventricular block, and decreased cardiac output and cardiac index in horse. Xylazine induces sedation and selective (S3 to Co) analgesia for at least 2 hours in cows. Xylazine significantly decreases heart rate, respiratory rate, rate of ruminal contractions, arterial blood pressure, PaO2, PCV, and total solids concentration, and significantly increases PaCO2, base excess, and bicarbonate concentration in cows. Xylazine severely depresses the N3 field (-75%) and completely abolishes the climbing fiber field (-100%) in the nonanesthetized, decerebrated rat. Xylazine- ketamine injections also severely depresses the N3 field (-75%) and nearly completely abolishes theclimbing fiber field (-90%) in the nonanesthetized, decerebrated