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Dieldrin and heptachlor were applied at 5.6 kg/ha and mixed 7.5 cm deep in the soil immediately before maize planting on a 0.68-ha watershed at Coshocton, Ohio, on April 30,1969. Vapor density profiles up to 4 m above the ground were measured on 7 days between May 2 and October 16. Vertical flux densities were calculated from eddy diffusion coefficients determined from simultaneous micrometeorological observations. Maximum flux intensities of 4.0 g/ha per day of dieldrin and 5.0 g/ha per day of heptachlor were observed on June 26th. Marked diurnal variations with noonday maxima were observed. Flux intensities declined to low values in October. Calculated seasonal losses were 199 g/ha of dieldrin and 383 g/ha of heptachlor.The importance of volatilization as a significant pathway for organochlorine insecticide loss from soils was noted by Lichtenstein and Schultz (1961). Later, Lichtenstein et al. (1964) showed that losses of aldrin and dieldrin were greatly reduced when the insecticides were incorporated to the 4 in. depth in the soil than when they remained on the surface without cultivation; they attributed this difference to the higher evaporation of the exposed material. Toxic concentrations of insecticide vapors in the air over soils treated with aldrin, heptachlor, and other insecticides were demonstrated by Harris and Lichtenstein (1961) who also showed that the vapor concentration, measured in terms of toxicity, was affected by temperature, humidity, and airflow. Spencer et al. (1973) reviewed measurements

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