The impact of elevated tropospheric ozone (O3) on the quality of spring oilseed rape (Brassica napus) and broccoli (Brassica oleracea) was assessed during a three year experiment. Current ambient O3 levels were compared to an increase of 20 and 40 ppb during 8 h per day over the entire growing season. Our results provide clear evidence that O3 has an influence on the qualitative attributes of the harvested products of these Brassica species. The protein concentration was significantly increased in response to O3. There was a shift in the fatty acid composition of the vegetable oil derived from seeds of oilseed rape. In rapeseed oil the observed decrease in vitamin E content was due to a reduction of g-tocopherol . a-TOC, the most active form of vitamin E in humans, was not influenced by O3. There was no change in the glucosinolate (GLS) content of oilseed rape seeds. In broccoli an important shift occurred from indolic to aliphatic GSLs although the total GSL concentrationwas not changed. The increase in the aliphatic/indolic GSL ratio may be important in relation to the anticarcinogenic properties of these vegetables. The results with regard to food and feed quality and human health are discussed.