Objective This clinical trial attempted to evaluate the potency, onset and duration of action of cis-atracurium in dogs.Animals Twenty dogs aged between 1 and 15 years and weighing between 15 and 85 kg admitted for a variety of elective, surgical procedures under general anaesthesia.Materials and methods Following induction of general anaesthesia, the effects of an intravenous loading dose of cis-atracurium (0.1 mg kg−1) were evaluated by counting visual responses to train of four (TOF) nerve stimulation. Incremental doses of 0.02 or 0.04 mg kg−1 cis-atracurium were administered when the first of four responses to TOF stimulation was present.Results An initial dose of 0.1 mg kg−1 eliminated all four TOF responses in 18 out of 20 dogs. The same dose, repeated 10 minutes later in two animals in which blockade was incomplete, abolished all responses. In dogs receiving 0.1 mg kg−1 cis-atracurium neuromuscular blockade lasted 27.2 ± 9.3 minutes. Up to six incremental doses were given in individual animals; incremental doses appeared to be noncumulative. No untoward side-effects were observed with the use of this drug. There was considerable variation between individuals in response to cis-atracurium.Conclusions Cis-atracurium is an effective neuromuscular blocking agent in the dog, although its potency varies.Clinical Relevance Further studies are required to determine whether observed differences in potency are related to age, breed or sex. Cis-atracurium may prove useful in dogs with impaired renal and or hepatic function.