A well-known asymmetry exists in the bilingual masked priming literature in which lexical decision is used: namely, masked primes in the dominant language (L1) facilitate decision times on targets in the less dominant language (L2), but not vice versa. In semantic categorization, on the other hand, priming is symmetrical. In Experiments 1-3 we confirm this task difference, finding robust masked L2-L1 translation priming in semantic categorization but not lexical decision. In formulating an account for these findings, we begin with the assumption of a representational asymmetry between L1 and L2 lexical semantic representations, such that L1 representations are richly populated and L2 representations are not. According to this representational account, L2-L1 priming does not occur in lexical decision because an insufficient proportion of the L1 lexical semantic representation is activated by the L2 prime. In semantic categorization, we argue that the semantic information recruited to generate a decision is restricted by the task category, and that this restriction enhances the effectiveness of the L2 prime. In Experiments 4-6, these assumptions were tested in a within-language setting by pairing many-sense words (e.g., ''head'') with few-sense words (e.g., ''skull''). In lexical decision, robust priming was obtained in the many-to-few direction (analogous to L1-L2), but, no priming was obtained in the few-to-many direction (analogous to L2-L1) using the same word pairs. Priming in semantic categorization, on the other hand, was obtained in both directions. We propose the Sense Model as a possible account of these findings.