Because only 9.4% of depressions are recognized at initial evaluation by primary physicians, the diagnosis of depression is important. Forty percent of a group of mixed depressions will resolve in a month without treatment, and 70% will resolve with the use of tricyclic antidepressants. Research on plasma levels of tricyclic antidepressants suggest new clinical strategies for adjusting dosages; neurochemical studies may provide an appropriate selection process for choosing a tricyclic antidepressant.