Using a computer-assisted infrared optometer we studied the long-term accommodative behavior in a 31-year-old man whose eyes had been accidentally exposed to diisopropyl fluorophosphate vapor. The initial examination revealed a delay of accommodative relaxation in both quasi-static and dynamic measurements, which recovered within one month, and a characteristic behavior in dark focus of accommodation, that is, a repetition of prominent myopic shift followed by rapid relaxation. This abnormal dark focus of accommodation appeared more marked after the subject was forced to fixate on a near target at a distance of three diopters. These abnormalities in dark focus of accommodation were fairly reduced three months later, but myopic shift was detected even 13 months later. The findings suggest a close association between myopic shift in the dark focus of accommodation and parasympathetic excitation.