Even though lithium has been established as an effective agent in the management of primary affective disorders, not all manic-depressive patients respond favourably to lithium therapy. Therefore we attempted to delineate lithium responders from non-responders in a group of 54 manic-depressive patients on the basis of an assessment which included 64 variables and the results showed that only two thirds were pure responders. Females, patients with prior manic episodes, onset of the illness initially with a manic episode, and premorbid psychothymic personality were all indicators of favourable long-term lithium response. Patients with retarded depression, severe anxiety, though disorder and those with higher scores on the Psychopathic Deviate and Paranoia scales of the MMPI were poor lithium responders. It should be noted, however, that only a few of the differences between responders and non-responders were statistically significant. Our study suggests a number of predictive variables for the identification of lithium responders.