It is a robust finding that ambiguous words are recognized faster than unambiguous words. More recent studies (e.g., Rodd et al. in "J Mem Lang" 46:245-266, 2002) now indicate that this "ambiguity advantage" may in reality be a "polysemy advantage": caused by related senses (polysemy) rather than unrelated meanings (homonymy). We report two lexical decision studies that investigated the effects of polysemy with new word sets. In both studies, polysemy was factorially manipulated while homonymy was controlled for. In Experiment 1, where the stimulus set consisted solely of concrete nouns, there was no effect of polysemy. However, in Experiment 2, where the stimulus set consisted of a mix of abstract nouns, verbs, and adjectives, there was a significant polysemy advantage. Together, these two studies strongly suggest that polysemy affects abstract but not concrete nouns. In addition, they rule out several alternative explanations for these polysemy effects, e.g., sense dominance, age-of-acquisition, familiarity, and semantic diversity.