The present report on the environmental effects of ozone depletion deals mainly with the direct effects of increased ultraviolet-B (UV-B) radiation on man and the environment. The report was written in 1989, the year that the Montreal Protocol came into effect. The Parties to the Protocol have agreed to specified limits on the production of certain gases that endanger the ozone layer. It was widely realized that the threat to the ozone shield was no longer theory. Occurrence of a "hole" in the ozone layer has been observed in the Antarctic region. At the time that the Protocol was signed, there were scientific data indicating that the limitations for the substances agreed upon were not sufficient for a recovery of the ozone layer. Parties advocated stricter limits and the inclusion of more gases. This report reviews and integrates scientific information on potential effects associated with various levels of stratospheric ozone decrease in an effort to assist decision makers, particularly those involved in the policy process. Clearly, the report would be the most useful if it could provide clear-cut quantitative predictions of the effects to be expected from the different policy options under consideration. The actual situation is rather far from that goal.