Two categorical perception studies were conducted in order to test the hypothesis that f0 is dominantly responsible for signaling the position of the accent, earlier known as 'stress', of Persian. We used disyllabic minimal pairs in which the accent was either on the second syllable, the word condition, or on the first, the word-plus-clitic condition. In both experiments, participants were presented with randomized stimuli in which the f0 had been manipulated and were asked to judge whether they heard a word or word-plus-clitic combination. In both cases, we found that the f0 manipulation switched judgement by 100%. Key words: pitch accent, clitic group, phonological word, categorical perception.