The sedative and physiological effects of intravenous romifidine at 0, 20, 40, 80 and 120 micrograms/kg were investigated in five clinically normal adult male beagle dogs in a blind study using a Latin square design. Following the injection of romifidine, the dogs became ataxic and stood with a wide-based stance, they exhibited signs of skeletal muscle relaxation and their heads were lowered. All the dogs became recumbent and there was a reduction in the heart and respiratory rates. Increasing the dose from 20 to 40 micrograms/kg, or higher, produced a significant reduction in heart rate. There was am increase in the sedation score following even low doses of romifidine, and although measures of sedation showed no differences among romifidine doses, subjectively, the higher doses produced a more consistent effect. Dogs given lower doses of romifidine regained a standing position more rapidly than following the higher doses, although this effect was not significantly different. A second blind study compared the sedative effects of intravenous romifidine, at 40 and 80 micrograms/kg, with medetomidine at 10 micrograms/kg in six adult beagles. The cardiopulmonary and sedative effects were not significantly different between all regimens, although medetomidine at 10 micrograms/kg appeared to be intermediate in effect between romifidine at 40 and 80 micrograms/kg. The sedative and physiological effects of romifidine in dogs appear to be similar to other alpha2-adrenoceptor agonists. Intravenous administration provided sedation which might be clinically useful.