Although Semantic Web service discovery has been extensively studied in the literature ([7], [12], [15] and [10]), we are far from achieving an effective, complete and automated discovery process. Using the incidence calculus [4], a truth-functional probabilistic calculus, and a lightweight brokering mechanism [17], the article explores the suitability of integrating probabilistic reasoning in Semantic Web services environments. We show how the combination of relaxation of the matching process and evaluation of web service capabilities based on a previous historical record of successful executions enables new possibilities in service discovery.