The angular tricyclic analog of melatonin, 8-methoxy-6-oxo-3,4,6,7-tetrahydro-1H,5H-azocin[4,5,6-cd]indole (IV) as well as the linear “dehydromelatonin” viz., 5-methoxy-1-acetyl-2,3-dihydropyrrolo[2,3-b]indole (VI) had retained only tiny fractions of the activity of melatonin. The lactam IV and the corresponding amine V showed no major CNS effects in mice and cats. © 1969, American Chemical Society. All rights reserved.