From 1972 to 1977, the authors observed 156 patients with primary esophageal motility disorders which caused such a severe degree of dysphagia that treatment by pneumatic dilatation was deemed necessary. Before dilatation, 24% of the patients presented with motility disorders that did not fit well into the two classical disease entities, diffuse esophageal spasm and achalasia (absence of peristalsis with presence of lower esophageal sphincter (LES) relaxations or presence of peristalsis with absence of LES relaxations). After treatment with pneumatic dilatation, these "intermediate" forms constituted 45% of the motor disorders. This was due mainly to the reappearance, on manometric tracings, of peristaltic contractions and of LES relaxations. Radiologic and manometric observations suggest that in many patients, this "return of peristalsis" may be an apparent change in pressure pattern rather than a real change in motility. In 6 of the 156 patients, a deterioration of the esophageal motility disorder was observed, which was characterized by the loss of peristalsis and of LES relaxations over a period of a few months or years. The frequent occurrence of intermediate types of motility disorders and the transition from diffuse spasm to achalasia suggest that achalasia and diffuse esophageal spasm are part of a spectrum of related motor disorders.