“Differences in Nocturnal Melatonin Secretion between Melancholic Depressed Patients and Control Subjects”, 1985-07 (; backlinks):
The authors took multiple serum samples for measurement of melatonin between 4:30PM and 7:30AM in 7 male depressed patients with melancholia and 5 healthy male control subjects and found that:
melancholic patients had a statistically-significantly lower rise of melatonin. They also compared a second, separate group of 14 women and 5 men suffering from melancholic depression with 7 healthy male control subjects and 9 depressed women without melancholia. The melancholic patients had a statistically-significantly lower concentration of serum melatonin at 11:00PM than either the control subjects or the non-melancholic depressed patients.
These findings support the possibility that the functioning of the pineal gland is altered in these patients.