Abstract: We argue that Brazilian Portuguese (BP) affixes can be divided in (at least) two groups according to their prosodic behavior: true affixes are prosodically integrated to the base, while compositional affixes are considered independent prosodic words. Aiming to find empirical evidence to sustain this distintion, we investigate two questions: (i) Can we find acoustic patterns in derived words to differentiate true and compositional affixes? (ii) Are there psycholinguistic evidence to sustain that these two groups are accessed differently in our lexicon?. In order to answer these questions, we developed two experimental paradigms. The first one is an acoustic analysis which compares duration in syllables and V-V units of derived words. In this experiment, syllables showed increase in duration towards the stressed position for all conditions, while V-V units seem to differentiate the two types of morphological formations. The second one is an eye tracking experiment with lexical decision task to describe fixations, saccades and level of accuracy in derived words and nonce words. Our main results show that compositional words presented longer total time of fixation in the eye tracking analysis and longer and less accurate answers in the lexical decision task, what sustains the hypothesis that the two categories behave differently Ver menos