A mail survey of 151 Iowa farmers with membership in Practical Farmers of Iowa, a sustainable agriculture organization, was used to examine the attitude-behavior relationship of these farmers and the role social influences play in this relationship. Attitude and social influence scales were developed, as well as a chemical input index that measures commitment to sustainable practices. Results indicate that, when controlling for explanatory factors, the attitude-behavior relationship is moderate and the social influences examined do not facilitate this relationship. Level of participation in sustainable or conventional organizations was not significant for this group. Use of conventional information sources was found to be a significant predictor of actual chemical usage, apparently regardless of attitudes. Implications for educational programs and policies are discussed.