The current widespread use of ester and amine formulations of 2,4–dichlorophenoxyacetic acid (2,4–D) and/or 2,4,5–trichlorophenoxyacetic acid (2,4,5–T) has made apparent the potential vapor hazard of these herbicides in their injury to susceptible crop plants growing nearby. A method used for evaluating the volatility of proprietary formulations was reported previously (1,2) using temperatures of 70° to 75° F. At this “normal” temperature eighty commercial ester preparations representing thirty-one different formulations of 2,4–D and/or 2,4,5–T showed, conclusively, that esters such as the isopropyl, butyl, ethyl, amyl, and pentyl individually or in mixture were volatile; and the iso-octyl, butoxyethanol, tetrahydrofurfuryl, polypropylene glycol, and propylene glycol butyl ether esters were low volatile. These formulations do not comprise all the commercial preparations tested but are given only to indicate the extent of volatility found for 2,4–D and 2,4,5–T ester herbicides commonly available on the market.