1. A tabulation of "essential" and helpful criteria for the diagnosis of familial dysautonomia is presented. The importance of accurate diagnosis is stressed. 2. Two cases where the diagnosis of familial dysautonomia was strongly suggested but was not justified are presented by way of contrast to the typical syndrome. 3. Current literature offering new observations of a pharmacological, physiological and anatomical nature is reviewed. Some of these appear to offer important new diagnostic criteria as well as bases for hypotheses for the pathogenesis of the disorder. 4. An attempt to synthesize the various findings is made. It is apparent that the basic functional defect has not yet been identified, though a humoral anomaly, very possibly enzymatic, still seems a reasonable interpretation of the underlying cause of the physiological abnormalities reported.