We describe two patients and a previously reported patient who acquired unique pendular vergence oscillations of the eyes and concurrent contractions of the masticatory muscles, i.e., oculomasticatory myorhythmia (OMM). The smooth disjunctive eye movements cycled with a frequency of 0.8 to 1.2 Hz. An analysis of peak velocities (15 to 200 degrees/sec) with respect to peak amplitudes (5 to 25 degrees) revealed dynamics characteristic of normal vergence movements. The pathological alterations resulting in pendular vergence oscillations implicate a separately functioning, physiologically normal vergence system within the brainstem. In addition to paralysis of vertical gaze, each patient also experienced progressive somnolence and intellectual deterioration. An intestinal biopsy in 1 patient established a diagnosis of Whipple's disease, which led to appropriate treatment and amelioration of the OMM. A pathological diagnosis of Whipple's disease of the central nervous system was made in the other 2 patients; results of an intestinal biopsy in one of these patients were normal. No patient had palatal myoclonus, and olivary pseudohypertrophy was not found in two autopsy examinations. Thus, OMM is a distinct movement disorder and has been recognized only in Whipple's disease. We conclude that patients with OMM should be treated presumptively for Whipple's disease of the central nervous system, even if a jejunal biopsy is normal.