This paper reports a laboratory experiment that examines price formation in the single call market. The experiment design is intended to enhance the predictive power of the Bayesian Nash equilibrium (BNE) theory for this trading institution. The data support several qualitative implications of the BNE, especially when subjects compete against Nash 'robot' opponents, but subjects' behavior is not as responsive to changes in the pricing rule as the BNE predictions. Offers tend to reveal more of the underlying values and costs than predicted, particularly when subjects are experienced. A simple learning model accounts for several of the deviations from BNE.