This paper presents the results of a phonological study of primary stress in Wichí, a Mataguayan language spoken in the Gran Chaco. In addition, it analyzes some word formation processes where morphological information conditions the assignment of stress. The Wichí rhythmic pattern consists of parsing the word into binary iambic feet from left to right. The lengthening of vowels occurs to enforce the optimal structure of the iambic foot. Primary stress is applied to the head of the rightmost foot in the phonological word. The same stress pattern is applied to base words (monomorphemic), words with affixes and/or clitics, and compounds. However, the addition of a group of extrametrical suffixes (locative/directional) and the word formation p...