This study investigated whether a prior context influenced lexical access as indexed by participants' electrophysiological response in the N1 from 132 to 192 ms poststimulus. Ambiguous, high-frequency (HF), and low-frequency (LF) words were presented in neutral and biasing contexts. Event-related potentials (ERPs) for ambiguous words were compared with those for unambiguous HF (word form) and LF (word meaning) control words. Word frequency effects in the N1 extended previous ERP findings. A marginal effect of context for LF words provided electrophysiological support for the context-by-frequency interaction shown in reaction time paradigms. In neutral context, responses to ambiguous words were comparable to responses to HF words, and in biasing context (where context instantiated the subordinate sense), responses to ambiguous words were comparable to responses to LF words. The results establish temporal parameters for the early operation of context in lexical access. These constraints are more consistent with an interactive than a modular account.