Medetomidine and fentanyl-droperidol (Innovar-vet) were assessed over a three hour period in 80 healthy dogs. Following physical examination, electrocardiogram (ECG), arterial blood sample analysis, and dynamometer pressure threshold (analgesia score), the dogs were randomly assigned to one of four treatments: Miv--medetomidine (750 micrograms/M2) administered intravenously (IV), Mim--medetomidine (1000 micrograms/M2) administered intramuscularly (IM), Iiv--Innovar-vet IV (0.05 mL/kg) or Iim--Innovar-vet IM (0.1 mL/kg). All assessments were carried out by a single individual unaware of the treatment used. Objective assessments included temperature, heart and respiratory rates, analgesia score, arterial blood gases, acid-base and lactate levels. Subjective evaluation included degree of sedation, response to various clinical procedures, noise responsiveness, posture, and the incidence of side effects. Onset and duration of effect were also recorded. The ECG strips were assessed for arrhythmias. Data was analyzed using a 3-way analysis of variance for continuous variables and a Chi-square analysis of frequencies. A p value < or = 0.05 was considered significant. Medetomidine-treated animals had a decreased respiratory rate, longer duration of analgesic effect, increased incidence of bradycardia, vomiting and twitching, were less noise responsive and shivered less throughout the study. An increased incidence of second degree heart block with Miv (15 min), a delayed onset and recovery with Mim and increased lactate levels following Iiv (15 min) were observed. No differences were found in other measurements and good to excellent chemical restraint was produced with all treatments in 65% or more cases.