The possibility that separation of a categorical depressive disease (‘melancholia’) from remaining depressive disorders can be improved by assessment of mental state signs was examined in patients treated by representative Sydney psychiatrists and patients referred to a specialised mood disorders unit. A set of signs, principally assessing retardation, was derived within the two samples by principal-components and latent-class analyses. Scores were significantly correlated with clinical, DSM–III, and RDC diagnoses, and appeared independent of severity, suggesting that melancholia can be defined phenomenologically. Scores were also associated with several ‘validating’ factors. Comparative analyses of a refined list of melancholia symptoms suggested that ratings of defined signs are likely to have greater capacity than symptom ratings to differentiate melancholia from residual depressive disorders.