In EuroSpeech95, we presented the first version of Sethos, the speech understanding system which has been developed at the UPC. In this paper some improvements are incorporated at different levels of Sethos: language model, models of the semantic units and acoustic models. These improvements increase the percentage of correctly decoded sentences from 60% to 80%. Some experiments are presented to evaluate the influence of each information source on the final performance. Furthermore, the computational cost is analyzed arriving to an important conclusion: the configuration which gives the best performance is also the less expensive. The reason is that as better is the modeling, narrower is the beam of the search.