Insomnia is widely accepted as a leading feature of that illness designated by the number 301.1 in the International Classification of Diseases. The name given varies—“endogenous depression”, “manic-depressive psychosis/depressive type”, “melancholia” or “depressive illness”. The present generation of laymen (not to say some psychiatrists) use the word “depression” so freely in order to describe an unpleasant, unhappy mood, whether lasting or transient, that one may prefer the term melancholia, or at least “depressive illness”, to signify that condition which justifies the number 301.1. The adjective “endogenous” implies for many that environmental stress plays little or no part in the onset of the illness; we cannot accept that this is always so. The term “reactive” is used in several ways, generally to indicate that the state of unhappiness arises out of some external circumstance and that it would end when circumstances improved or the individual accepted the realities of practical life. The patients used in the present study were suffering from an illness of a kind which we believe may sometimes develop in the absence of severe environmental stress, while in others it may be clearly provoked by circumstances, but the illness, as it develops, may take on a form which becomes largely independent of the environmental circumstances and may continue even when the provoking factors are past; it has become an autonomous melancholia. It will be apparent that by autonomous melancholia we mean an illness shown by clinical experience to respond especially well to electroplexy.