Summary — An important parameter in evaluating the activity of a honeybee colony is given by the number of bees leaving and entering the hive as a function of time. The microprocessor-controlled counter described here presents many advantages over previous counting devices. The counter fits the standard hive measurement (10 combs), and provides access to the hive via 32 bi-directional channels. The very small infrared detectors in each channel are only 0.1 mm apart, and are controlled by an asynchronous sequential algorithm, which improves the counter's precision. Results of measurements of the daily activity of honeybee colonies under different conditions (normal, in the presence of pesticides, or during swarming) are presented.Apis mellifera / bee counter / flight activity / swarming / pesticides INTRODUCTION