The main goal of this paper is to provide empirical evidence, through a controlled experiment, of the influence of stereotypes when modelers, developers, and maintainers have to comprehend UML sequence diagrams. The comprehension of UML sequence diagrams with and without stereotypes was analyzed from three different perspectives: semantic comprehension, retention and transfer. The experiment was carried out with 77 fourth year undergraduate students of Computer Science from the University of Bari in Italy. The results obtained show a slight tendency in favor of the use of stereotypes in facilitating the comprehension of UML sequence diagrams, although it is not statistically significant. Further replications are needed to obtain more conclusive results.