The investigations employed in the diagnosis of oesophageal achalasia have been assessed critically. Although electromanometry contributes most to diagnosis and pinpoints with absolute precision the physiopathological elements that characterise the disease, radioisotopic study of oesophageal transit is an important diagnostic aid. More readily than any other, this technique permits morphofunctional evaluation in selected patients; it also represents the most physiological investigation and the best tolerated and, second only to manometry, the most reliable. Oesophagography with baritate meal and oesophagoscopy also play a diagnostic role in oesophageal achalasia. The former makes it possible to document the cardial stop and the presence or otherwise of mega-oesophagus, the second excludes the presence of organic dysphagias and also has a therapeutic use because cycles of dilatation of the oesophago-cardial junction can be carried out.