The objective of this study was a comparison of pentobarbital and T 61 in the euthanasia of cattle. 397 cattle of different ages and breeds which had to be euthanised in the Clinic for Ruminants were enrolled. Following clinical examination, euthanasia was performed by intravenous injection of either 40 mg pentobarbital per kg body weight (BW) (0.1 ml Eutha 77) or 0.1 ml T 61/kg BW. The intervals between the beginning of injection and the following events were noted: collapse of the animal, cessation of respiration, cessation of cardiac action, disappearance of the palpebral and corneal reflexes, and maximum dilatation of the pupils. These post-injection events occurred significantly earlier with Eutha 77. In addition, events like excitations and vocalisations were recorded. Excitations occurred twice as often with T 61 (in 34% of cases) than with Eutha 77 (17%), and strong excitations (grade 3 of 3) were also more frequent with T 61 (9.8%) than with Eutha 77 (3%). Vocalisations were less frequent (30%) with T 61 than with pentobarbital (39%), but this difference was not significant. Severe vocalisations occurred very rarely. With both drugs, intervals between the beginning of injection until cessation of reflexes were longer in older animals. Following injection of Eutha 77, cessation of the corneal reflex and maximal dilatation of the pupils occurred earlier in cattle with severe disturbance of the general condition than in cattle with lesser disturbance; in the T 61-group this difference was only significant for the interval until cessation of the corneal reflex. In anaesthetized patients euthanized with T 61 cessation of cardiac action and respiration occurred earlier than in patients that were not under general anaesthesia when euthanized; in the Eutha 77 group, the difference was significant only for the interval until cessation of cardiac action.