Abstract. We propose a probabilistic document retrieval model based on Bayesian networks. The network is used to compute the posterior probabilities of relevance of the documents in the collection given a query. These computations can be carried out efficiently, because of the specific network topology and conditional probability tables being considered, which allow the use of a fast and exact probabilities propagation algorithm. In the initial model, only direct relationships between the terms in the glossary and the documents that contain them are considered, giving rise to a Bayesian network with two layers. Next, we consider an extended model that also includes direct relationships between documents, using a network topology with three layers. We also report the results of a set of experiments with the two models, using several standard document collections.