BACKGROUND: Production of passive sentences is often impaired in agrammatic aphasia and has been attributed both to an underlying structural impairment (e.g., Schwartz, Saffran, Fink, Myers, & Martin, 1994) and to a morphological deficit (e.g., Caplan & Hanna, 1998; Faroqi-Shah & Thompson, 2003). However, the nature of the deficit in passive sentence production is not clear due to methodological issues present in previous studies. AIMS: This study examined active and passive sentence production in nine agrammatic aphasic speakers under conditions of structural priming using eyetracking to test whether structural impairments occur independently of morphological impairments and whether the underlying nature of error types is reflected in on-line measures, i.e., eye movements and speech onset latencies. METHODS #ENTITYSTARTX00026; PROCEDURES: Nine participants viewed and listened to a prime sentence in either active or passive voice, and then repeated it aloud. Next, a target picture appeared on the computer monitor and participants were instructed to describe it using the primed sentence structure. OUTCOMES #ENTITYSTARTX00026; RESULTS: Participants made substantial errors in sentence structure, i.e., passives with role reversals (RRs) and actives-for-passives, but few errors in passive morphology. Longer gaze durations to the first-produced noun for passives with RRs as compared to correct passives were found before and during speech. For actives-for-passives, however, this pattern was found during speech, but not before speech. CONCLUSIONS: The deficit in passive sentence production does not solely arise from a morphological deficit, rather it stems, at least in part, from a structural level impairment. The underlying nature of passives with RRs is qualitatively different from that of actives-for-passives, which cannot be clearly differentiated with off-line testing methodology.