Three hypotheses from von Ditfurth''s biological theory of depression are reviewed and tested on 300 patients. The 1st hypothesis of the initial vegetative stage of endogenous depression and the 2nd hypothesis that the autonomic disturbances and the disturbances of vital feeling are of equally important rank, are both supported by the findings. The validity of both theses is expanded in relation to depression in general. Corroboration of the 3rd hypothesis, that certain autonomic disturbances correspond to certain psychic disturbances meets with intractable difficulties. In conclusion, on therapeutic and prognostic grounds, it is suggested that the vegetative state should be taken into account when the diagnosis is formulated.