This paper reports a laboratory experiment designed to examine the price formation process in a simple market institution, the single call market. The experiment features random values and costs each period, so each period generates a new price formation observation. Other design features are intended to enhance the predictive power of the Bayesian Nash equilibrium (BNE) theory developed recently for this trading institution. We find that the data support several qualitative implications of the BNE, but that subjects' bid and ask behavior is not as responsive to changes in the pricing rule as the BNE predictions. Bids and asks tend to reveal more of the underlying values and costs than predicted, particularly when subjects are experienced. Nevertheless, observed trading efficiency falls below the BNE prediction. The results offer more support for the BNE when subjects compete against Nash "robot" opponents. A simple learning model accounts for several of the deviations from BNE.