Honey bees entering and leaving their hive were registered with photoelectrical counters. By using this method it was possible to measure flight activity cycles of high and low levels. Considering the effect of reproduction and mortality rates, the observed rhythm of activity could be attributed to the phases of the moon. Observations of outdoor flight activity in Morocco, under weather conditions permitting, from June to October and indoor flight activity in a controlled environment rearing room in Germany from November 1968 to August 1970 had the following results: