The therapeutic efficacy of praziquantel, pyrantel embonate and febantel (Drontal Flavour Plus) for three and five consecutive days was evaluated for treating naturally acquired giardiasis in dogs. In the study, 24 dogs naturally infected with Giardia were divided into three groups of eight dogs each. Dogs were treated at the recommended dosage for three or five consecutive days, and a control group remained untreated. Faecal samples from each dog were submitted to coprological examination from day-4 to -2 and at days 5, 7, 9 and 11. Faecal consistency was also assessed daily to study end. All dogs in the control group remained positive until study end. Giardia cysts were not detected in faeces of six of the eight dogs in the group treated on three consecutive days, and in faeces of five of the dogs in the group treated on five consecutive days. Unformed to diarrhoeic faeces were more often reported in dogs in the untreated control group than in dogs in both treatment groups. Efficacy of treatment for five consecutive days was not statistically better than treatment for three consecutive days.