Two different willingness-to-pay responses are compared-willingness to pay to avoid loss of air quality and willingness to pay to obtain gains in air quality. Contingent valuation data were used to estimate bid functions for these two types of responses for visibility and health. Comparison of the estimated models indicates that, in addition to magnitude differences, gains and losses for visibility and health are affected differently by health status, risk perceptions, and other risk-related variables. Results for the loss measure are more reliable in terms of variability of response and econometric modeling.