This paper describes a direct revelation mechanism for eliciting decision makers' introspective beliefs on sets of subjective prior or posterior probabilities. The proposed scheme constitutes a revealedpreference procedure for measuring the inclination of decision makers to choose one alternative over another modeled by Minardi and Savochkin (2015).Keywords: Knightian uncertainty; second-order beliefs; probability elicitation; random choice; introspective beliefs; graded preferences.JEL classification numbers: D80, D82, D83 * Department of Economics, Johns Hopkins University, Baltimore, MD 21218, USA. e-mail address: karni@jhu.edu. I am grateful to two anonymous referees for their useful comments and suggestions.