The tricyclic amitriptyline and the selective serotonin reuptake inhibitor fluoxetine have distinct actions in animal models of anxiety, though both antidepressants are used against anxiety disorders. Grooming behavioural sequencing, rather than its general "activity" measures, has been suggested to measure effectively the pharmacologically induced anxiolytic and anxiogenic-like effects in rats and mice. In the present study, the acute effects of amitriptyline and fluoxetine on anxiety were re-evaluated by using an analysis algorithm in novelty-induced grooming activity in rats. Additionally, the effects on anxiety-like behaviour in the hole board were examined. Amitriptyline (5 and 10 mg/kg) and fluoxetine (5 and 10 mg/kg) not only affected the traditional gross measures, but also produced changes in incorrect transitions and regional distribution of grooming behaviour. High dose of fluoxetine showed an anxiogenic-like profile by reducing head dipping and rearing in the hole board. Depending on the effects on the behavioural microstructure of grooming activity, present findings imply that amitriptyline may possess anxiogenic and fluoxetine may possess anxiolytic activities. However, measures of hole board do not fully support this suggestion. (C) 2008 Elsevier B.V. All rights reserved.