Dysphagia is often present early, with varying degrees of involvement, in patients with myasthenia gravis. Twenty-five patients with a clinical status of myasthenia gravis were graded according to a modified Osserman classification and the esophageal manometric results were reported according to their clinical status. The results were also compared with those in 20 normal control subjects. Twenty-four patients (96%) had abnormal motility. The only patient who was in class I had a normal tracing. There was no significant difference in function of the lower esophageal sphincter, but a significant decrease in mean amplitude (15.1 +/- 6.1 versus 29.7 +/- 4.7 mm Hg) and a prolongation in mean duration of the peristaltic wave (7.4 +/- 2.8 versus 4.5 +/- 0.2 seconds) was noted in the upper esophagus. The cricopharyngeal sphincter pressure also showed a significant decrease (23.4 +/- 9.5 versus 43.1 +/- 3.1 mm Hg), but relaxation and coordination were good. The mean amplitudes, mean duration of peristaltic waves, and cricopharyngeal pressures between the myasthenic and control populations were statistically significant, with a p value of 0.001. Besides this, frequent spontaneous contractions, simultaneous contractions, and biphasic repetitive contractions typical of peristaltic dysfunction were also found in myasthenic patients. Motor dysfunction of the esophagus as assessed by manometric study correlates well with Osserman's modified clinical classification.