Re-entrainment of the circadian rhythms of plasma melatonin in an 11-h eastward bound flight

We investigated the re-entrainment of melatonin rhythm in an Il-h eastward- bound flight. Eight male subjects participated in the present study. Blood sampling was carried out once before the Right and twice after the flight. During the daytime the subjects were exposed to natural zeitgeber outdoors on the day except the blood sampling. Seven of eight subjects showed antidr omic re-entrainment, and the other subject showed orthodromic re-entrainmen t. The intensity of natural day light in New York amounted to 20 000 Ix. As for the direction of the re-entrainment in New York the antidromic re-entr ainment is naturally dominant.