In an open uncontrolled study, 30 dogs with atopy were given six different antihistamines over a period of 10 weeks. During the first six weeks the dogs were given each of the antihistamines, hydroxyzine, trimeprazine, chlorpheniramine, clemastine, promethazine and cyproheptadine for a seven-day period. The order of drug administration was randomised in each case. After assessment of clinical improvement, based on the drug's ability to control pruritus, the most successful drug was given for a further four weeks. Where several drugs performed equally well in the control of signs, the second drug was selected on cost, ease of administration and lack of side effects. More than 60 per cent of the dogs benefited from antihistamine therapy and few side effects were noted. Hydroxyzine in this trial, proved to be the most effective antihistamine in controlling pruritus, although all of the drugs were shown to have the ability to control pruritus in some dogs.