This paper presents a formal theoretic framework to analyze credit union interest rates on loans and savings deposits. The unique motivational and institutional features of a credit union, in particular its structure as a financial service cooperative, are used to develop the objective function. This is based on a comparison of the credit union's rates to alternatively available market rates and includes parameters to recognize the possibility of borrower-saver conflict. The principal result is that the optimal rates and reactions to exogenous changes depend critically on the preference of the organization toward financial gain to the borrowing and saving members.