Glutamate concentration was determined in serum from endogenous and neurotic depressive patients, in persons with schizophrenia or schizoaffective disorder, and in normal subjects. The mean serum glutamate level in the endogenous and neurotic depressive patients was found to be significantly higher than in any of the other groups. No other statistically significant differences were found. Statistical analysis revealed that the elevated serum glutamate concentration in the endogenous and neurotic depressive patients was probably caused by medication. These results are discussed in view of the effect of antidepressants upon the serum glutamate in the affective disorders.

The levels of total and free tryptophan were determined in the plasma of 34 endogenous depressives, 20 neurotic depressives and 25 healthy volunteers. Whilst the levels of total tryptophan were not different in the three groups, the level of free tryptophan was reduced in both endogenous and neurotic depressives.