To investigate the relationships between the immune apparatus, major depression, and HPA-axis and noradrenergic activity, the authors measured the lymphocyte stimulation responses to the mitogens phytohaemagglutinin (PHA), pokeweed mitogen (PWM) and concanavalin A (CON A), post-dexamethasone cortisol (DST) values and 3-methoxy-4-hydroxyphenylglycol (MHPG) excretion in 24-hour urine samples from 48 patients. We found that lymphocyte responses to PHA and PWM in melancholic and psychotic depressives were significantly lower than in minor depressives. The lymphocyte responses to PHA, PWM and CON A showed significantly negative correlations with age, DST results and HRSD score. Responses to PHA were significantly negatively correlated with MHPG excretion. Up to +/- 33% of the variance in the three mitogenic lymphocyte responses could be explained by canonical correlation with age, DST results and MHPG values.