The provisions in the Montreal Protocol and its amendments in London (1990) and Copenhagen (1992) have brought about a marked decrease in production and use of ozone depleting chemicals. However, the ozone layer is still becoming thinner, and this is expected to continue until about 1998. Thereafter, a gradual recovery is predicted, but the layer will be damaged for half a century to come. The present assessment deals with the consequences during the coming decades: the changes in solar ultraviolet radiation reaching the Earth's surface, and the effects on humans, animals, plants, micro-organisms, air quality and materials. A welcome new element, compared with the earlier assessments, is a special chapter on biogeochemical cycles. The main questions from a policy point of view are now: what will be the most important effects, and what can be done to prevent or mitigate these?