Abstract
A five-cluster typology of severely ill depressives was developed and at least partially validated. The relationship between biological and psychological processes in the manifestation of chronic, so called "treatment resistant" depression was addressed through the use of measures of both these classes of variables. Severe, chronic depressive illness appears to become labelled "treatment resistant" when it encompasses multiple syndromal dimensions and/or atypical symptomatology. Biological, characterological, symptomatological and demographic variables appear to comprise the dimensions on which subtypes of this population fall. Methodologic and theoretical issues were discussed.