Whether behavioral and psychological factors are related to the response to light therapy and the onset of a novel depressive episode has been studied in patients with Seasonal Affective Disorder (SAD) and a control group. The interaction between 24 acute SAD patients and an interviewer was analyzed with ethological methods. It was found that nonverbal aspects of an interaction, before light therapy, are related with the response to light therapy. Moreover, in another study coping behaviour and neuroticism has been assessed in 29 SAD patients in remission (early autumn) and their controls. It was found that SAD patients are more neurotic and react with more depression and anger/irritation to stressful events than controls. The more anger/irritation they report in early autumn, the earlier they become depressed in the next late autumn and winter. Results are in line with interactional theories of depression and suggest that behavioral and psychological factors may mediate the response to light therapy and the onset of a novel depressed episode.