According to interpersonal theories on depression, the type of interaction between depression-prone subjects and their social environment plays a causal role in the development and course of depression (e.g. Coyne et al.). So far, interpersonal theories have been tackled mostly by psychometrical methods. However, non-verbal behaviour plays an important role in human social interactions. It is assumed that 60-65% of human communication is non-verbal. Ethological observations have shown that non-verbal interpersonal behaviour of depressed subjects, as assessed prior to treatment, is related to treatment-response or subsequent course of depression. These results are in line with an interpersonal approach of depression.

In manic-depressive patients treated with lithium salts the transport of choline over the erythrocyte membrane is strongly inhibited, resulting in dramatically increased erythrocyte choline levels (for review see ref. 1). Whether or not there is a relationship between this effect and treatment response is not clear. Data on this issue are scarce possibly because the measurement of treatment response in lithium prophylaxis is very difficult and time consuming. Also the effect on erythrocyte choline is specific for lithium and not for manic-depressive illness. We will address here the question of a possible relation between erythrocyte choline and clinical effects of lithium.

The probability that an individual will suffer from a major depressive episode is often considered to be influenced by risk factors such as gender, premature parental loss, exposure to pathogenic parental rearing, personality, a history of traumatic events, a previous history of major depression, low social support, recent stressful life events and difficulties and predisposing genetic influences. Although several studies suffer from methodological limitations, major depression (endogenous depression) is regarded as a multifactorial disorder and understanding its etiology requires the rigorous integration of several risk factors.