Depletion of the stratospheric O3 layer should result in enhanced levels of ultraviolet-B (UV-B) radiation at the earth's surface compared to present, with potentially damaging effects on biological systems. The paper briefly summarizes some key findings for UV-B effects on terrestrial ecosystems, and describes an ecological risk assessment model applicable to the impacts of enhanced UV-B on those systems. Potential use of the model is evaluated in terms of a project to determine the risk from UV-B on irrigated rice in southern and eastern Asia. Preliminary results from the UV-B treatments show no direct effects on yield. However, in terms of indirect effects of UV-B, preliminary results from IRRI and Washington State University suggest that UV-B can alter the susceptibility of rice plants to disease and affect the disease fungus itself.