Soybean was grown from seed in a greenhouse under ultraviolet-B (UV-B, 280-320 nm) radiation supplied by filtered FS-40 sunlamps. On a weighted, total daily dose basis these plants received either 0 (control) or 2875 effective J m-2 day-1 UV-BBE. When weighted with the generalized plant action spectrum, this simulated the solar ultraviolet-B irradiance expected to occur at College Park, Maryland, USA (39 degrees N) in the event the global stratospheric ozone column is reduced by 23%. The effects of ultraviolet radiation on the photosynthetic recovery from water stress were measured with an infrared gas analyzer. These effects were examined in plants which were either well-watered or previously preconditioned to water stress, during two distinct phenological stages of development.