Depression occurs in oral contraceptive therapy, in pregnancy, and during premenstrual tension is in no doubt, although it must be stated that few investigators involved themselves in the biochemical investigation of depression occurring in pregnancy and the menopause until "the pill" arrived as a form of therapy. The work culminates with the demonstration that in a double-blind cross-over trial, a group of women on the pill, who showed evidence of vitamin B6 deficiency, responded clinically to the effect of extra pyridoxine hydrochloride. The administration of l-tryptophan as a form of therapy in the relief of depression may have an effect on the hydroxylase, which is not pyridoxine dependent. As tryptophan can pass the blood-brain barrier, it may restore 5HT synthesis to normal. The rationale of the use of the drugs, the monoamine oxidase inhibitors, for control of endogenous depression is based on the concept of restoring normal brain 5HT levels to normal, although there is much dispute over their value.