A first field study was conducted to investigate the possible adverse effects that seeds dressed with neonicotinoid insecticides pose to honeybees during sowing. It was observed that in the exposure hives bee mortality increased on the day of sowing and that the number of foraging bees decreased the days after the sowing. The corn sowing posed a significant threat to honeybees, with thiamethoxam being the most probable toxic agent. A theoretical contact exposure was calculated for a bee when flying over the sown fields, revealing a dose of 9.2 ng bee(-1) close to the contact LD(50) of thiamethoxam.