In order to study the deposition of infective spores of barley powdery mildew in Denmark during the spring, young barley plants were placed at various sites in 1977 and exposed to ambient conditions for several hours when air mass movements in south to north directions had been predicted. The exposed plants became infected at the southernmost exposure sites on each exposure day: April 28 and May 5 and 6. Only a slight decrease in the number of barley mildew colonies was noted in the south to north direction at distances varying from about 30 to 100 km from the southernmost site, after which an abrupt decrease to zero was recorded at the next more northerly site. Possible causes for the sudden cessation in spore deposition are discussed. If a sudden decrease to zero of deposited conidia generally takes place at different Iaütudes in Denmark in the spring, then the sum of deposited conidia during the period late April to early May might well exhibit a gradual decrease in a south to north direction corresponding to the earlier reported gradual decrease in the number of mildew colonies in barley fields in the period late May to early June.