Previous studies that attempt to relate environmental to financial performance have often led to conflicting results due to small samples and subjective environmental performance criteria. We report on a study that relates the market value of firms in the S&P 500 to objective measures of their environmental performance. After controlling for variables traditionally thought to explain firm-level financial performance, we find that bad environmental performance is negatively correlated with the intangible asset value of firms. The average ‘intangible liability’ for firms in our sample is $380 million—approximately 9% of the replacement value of tangible assets. We conclude that legally emitted toxic chemicals have a significant effect on the intangible asset value of publicly traded companies. A 10% reduction in emissions of toxic chemicals results in a $34 million increase in market value. The magnitude of these effects varies across industries, with larger losses accruing to the traditionally polluting industries.