This paper addresses primary stress in Brazilian Portuguese considering the sonority of vowels for the construction of feet. In our proposal, in words, as saci and urubu for example, primary stress foot is iambic because [i] and [u], when positioned at the end of a prosodic word, are considered good peak elements. A constraint against the positioning of i/u in the weak part of the foot, *T/i,u, ranked higher in the hierarchy, can explain how a trochaic language, like Brazilian Portuguese, can present iambic feet in some words
