Summary1A case of divergence excess combined with an esophoria is reported.2The prevailing theories regarding the nature of divergence excess are discussed.3It is shown that divergence excess is due neither to excessive stimulation of the divergence centre nor to an anomalous position of rest dependent on anatomic factors.4It is proposed to regard divergence excess as an anomaly of the postural tonus of the extrinsic muscular apparatus in an atavistic sense.5According to this view, the eyes are capable of maintaining one of two alternative postures:a more primitive divergent one, or a more recently acquired parallel one, depending on the degree of cortical control which is being exercised.