The purpose of this investigation was to test the assumption of asymmetric mapping between words and concepts in bilingual memory as proposed by the Revised Hierarchical Model (RHM, Kroll & Stewart, 1994). Twenty four Spanish-English bilinguals (experiment 1) and twenty English-Spanish bilinguals (experiment 2) were presented with pairs of words, one in English and one in Spanish, and asked to indicate whether or not the words had the same meaning. In half the trials the Spanish word preceded the English, and in the other half the English word preceded the Spanish. In each condition half of the words had the same meaning, and the experiment included both concrete and abstract word trials. Event-related potentials (ERPs) were used to examine lexical-semantic activation during word translation. As predicted, a direction-dependent translation asymmetry was observed in the magnitude of the N400 repetition effect. Specifically, the N400 effect was larger during backward translation (L2-L1) than during forward translation (L1-L2) in both groups of bilinguals. Results are considered in the context of different models of bilingual memory. (Contains 6 tables and 2 figures.)