When achalasia becomes far advanced and leads to esophageal resection, inflammation of the esophageal mucosa is almost universal. The histology of the esophageal mucosa in less advanced cases of achalasia has not been firmly established. We have studied endoscopic biopsies obtained during evaluation of patients with achalasia. Two to four endoscopic biopsies from the lower esophagus of 26 patients with manometrically verified achalasia were mounted on mesh, serially sectioned, stained, coded and interpreted by two independent observers using recognized criteria. The histological findings were correlated with clinical data. Ten of 26 patients had at least one abnormal biopsy. Five of these 10 patients had a previous Heller myotomy; another patient had several pneumatic dilatations, and two other patients had endoscopically proven candida infections. Of the 16 patients with normal histology, four had prolonged stasis, five had heartburn and one patient had both heartburn and stasis. Unless the patient with achalasia has had a Heller myotomy, balloon dilatation, or a candida infection, the esophageal mucosa on biopsy appears to be within normal limits, even in patients with years of esophageal stasis or complaints of heartburn.