The main goal of this study was to determine whether the phonological and semantic processing of words are similarly influenced by an increase in processing complexity. Thirty-six French-speaking young adults performed both semantic and phonological word judgment tasks, using a divided visual field procedure. The phonological complexity of words was controlled by varying their transparency, while semantic complexity was manipulated through prototypicality. As expected, processing complexity modulated semantic and phonological processing differently. The results revealed that an increase in processing complexity lessened the left-hemisphere advantage in semantics, but reinforced it in phonology. It is therefore suggested that right-hemisphere collaboration in complex language processing is profitable only when the particular kind of processing is not strongly lateralized to the left-hemisphere. The results are discussed from the perspective of interhemispheric collaboration. (Contains 2 figures and 1 table.)