Evaporation losses from spray droplets carried in an air stream Were measured by determining the increase in concentration of a previously dissolved chemical. The losses were correlated with the ambient wet-bulb depression, the distance traveled (time elapsed) before impingement, and the spray “fineness.” A brief discussion of the pertinent theories of evaporation, air stream dynamics, and droplet motion is given. The probable implication to pesticide spraying of the rather large volume losses that may occur is discussed.