BACKGROUND: Only a few studies have investigated neurophysiological substrates of phonological impairment in acute aphasia. Nonetheless, event-related potentials (ERPs) can provide a valuable complement for a sometimes problematic behavioural evaluation at this stage of stroke. We aimed to identify neurophysiological substrates of: 1) impaired phonemic contrast sensitivity during pre-attentive (Mismatch Negativity; MMN) and attentive (P300) phoneme discrimination and 2) recognition abilities of real words and pseudowords. METHODS: Auditory oddball tasks for phoneme discrimination (MMN, P300) and word recognition (N100, P200, N400) were administered during EEG acquisition and ERPs were analysed. Data of the aphasic patients were compared with previously developed normative data (Aerts et al., under review). RESULTS: Aphasic patients in the acute stage of stroke showed more preservation of place of articulation during phoneme discrimination. Voicing, and to a lesser degree manner of articulation, were the most vulnerable. There was a significant negative effect of attention. During word recognition, pseudowords elicited larger responses than real words in aphasic patients, though with an important delay compared to the norm group, which indicates some sparing of lexical processing. CONCLUSION: The currently used paradigms seem to be sensitive enough for neurophysiological, clinical evaluation of phoneme and word processing in acute aphasia.