Relatively high concentrations of surface ozone and the indication that ozone is the inciting agent in fleck injury to tobacco were reported previously (1). Considerable interest therefore attaches to weather parameters on the high-ozone days which may throw light on the source and on the physicochemical processes affecting the ozone level. A source in the direction of nearby Washington, D.C., and photochemical production of the oxidant are indicated. Days with appropriate wind direction but low peak ozone concentration are discussed in terms of coexisting weather parameters. The weather ensemble found on high-ozone days is considered in relation to instances of fleck injury for which peak ozone levels were not measured.