(1) A recent review of the pineal literature revealed that when hamsters are exposed to 24-hour light:dark (LD) cycles with less than 12 hours of darkness (summerlike, SLD), the nightly period of pineal melatonin synthesis (PPMS) begins close to the midpoint of the dark period ("midnight") and ends at lights-on irrespective of the length of the dark period or time of day presented.