Schmid-Burgk W, Kim J S, Lischewski R, Rassmann W
Arch Psychiatr Nervenkr (1970). 1981;231(1):35-9. doi: 10.1007/BF00342828.
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.