We consider a Bayesian approach to the comparison of two potency curves under shape constraints. This work arises from analyzing a data set collected in an economics experiment, which is designed to test whether experimenter observatio n influences play of the ultimatum game. Our method extends recent work in the nonparametric Bayesian analysis of bioassay problems when the prior constrains the form of the potency curve. A Markov Chain Monte Carlo method is used to calculate the posterior features of interest. Various extensions of the Bayesian model and other applications will also be discussed.