Neuroimaging studies of English suggest that speech comprehension engages two interdependent systems: a bilateral fronto-temporal network responsible for general perceptual and cognitive processing, and a specialised left-lateralised network supporting specifically linguistic processing. Using fMRI we test this hypothesis in Polish, a Slavic language with rich and diverse morphology. We manipulated general perceptual complexity (presence or absence of an onset-embedded stem, e.g. "kotlet" "cutlet" vs. "kot" "cat") and specifically linguistic complexity (presence of an inflectional affix, e.g. "dom" "house, Nom" vs. "dom-u" "house, Gen"). Non-linguistic complexity activated a bilateral network, as in English, but we found no differences between inflected and uninflected nouns. Instead, all types of words activated left inferior frontal areas, suggesting that all Polish words can be considered linguistically "complex" in processing terms. The results support a dual network hypothesis, but highlight differences between languages like English and Polish, and underline the importance of cross-linguistic comparisons. (Contains 3 tables and 3 figures.)