In this uncontrolled clinical study 12 investigators cooperated to evaluate the analgesic and sedative effect of detomidine (DORMOSEDAN; Farmos Group Ltd; Finland) in 234 horses with abdominal pain caused by colic. The study was designed to use each animal as its own control and to evaluate its response to the drug over a 60 min period. Detomidine was given intravenously (i.v.) once in 169 cases (167 horses, 1 mule, 1 donkey) at a dose of 20 micrograms/kg bodyweight (bwt), and to 65 horses at 40 micrograms/kg bwt. The higher dose was used predominantly in horses with severe pain which were more often in poor health and therefore given a poor prognosis. Sedation and analgesia, rated as satisfactory or highly satisfactory, was achieved in 96 per cent of cases, without obvious differences between doses, sex, breed and species. First clinical signs of sedation and analgesia were recorded within 2.5 and 3.2 mins, respectively, and deep sedation and analgesia were achieved by 4.2 and 5.1 mins. Objective evaluation of analgesia was based on clinical scores related to behaviour (eg sweating, kicking, pawing, head and body movement, stretching, lip curling, attitude and appetite). In five of seven of these parameters the 40 micrograms/kg bwt treatment scored higher initially (P < 0.001) and took longer to return to normal. Although most cases treated with 20 micrograms/kg bwt returned to almost normal levels by 15 mins, those treated with 40 micrograms/kg required 30 mins. Animals not responding to either dose of detomidine went to surgery and/or were destroyed. These involved intestinal strangulation, incarceration, and torsion or rotation of the intestinal tract. No differences were found between doses in the occurrence of side effects. As expected, heart rates and respiratory rates decreased and recovered slowly. Other side effects were recorded in approximately 37 per cent of cases and consisted of instability (27.1 per cent of all other side effects), sweating (14.5 per cent), cardiovascular abnormalities (arrhythmias: 15.1 per cent) and abnormal reactions to sensorial stimuli (6.6 per cent). Less than 20 per cent of the side effects were classified as 'strong' or 'very strong' and none was considered serious. No deaths were attributed to the drug.