In this paper, we propose a method based on Bayesian networks for interpretation of multimodal signals used in the spoken dialogue between a tour-guide robot and visitors in mass exhibition conditions. We report on experiments interpreting speech and laser scanner signals in the dialogue management system of the autonomous tour-guide robot RoboX, successfully deployed at the Swiss National Exhibition (Expo.02). A correct interpretation of a users (visitors) goal or intention at each dialogue state is a key issue for successful voice-enabled communication between tour-guide robots and visitors. To infer the visitors goal under the uncertainty intrinsic to these two modalities, we introduce Bayesian networks for combining noisy speech recognition with data from a laser scanner, which is independent of acoustic noise. Experiments with real data, collected during the operation of RoboX at Expo.02 demonstrate the effectiveness of the approach.