Injections and applications of hydrogen peroxide, peroxidase, and other chemicals evoked luminescence with variable success in three Atlantic lanternfishes of the family Myctophidae: Benthosema glaciale, Myctophum punctatum, and Notoscopelus kroeyeri. Electrical stimulation of the spinal cord and of isolated photophores resulted in only a few brief light responses in the first two species. Epinephrine injections evoked luminescence in the gonostomatid Maurolicus muelleri while injection and external application of hydrogen peroxide failed to produce a response in this species and in the stomiatid Stomias boa ferox. These and earlier data are discussed in terms of methodology and physiological states of the fish, biochemical systems involved, and luminescence control.