The present study focuses on the use of thinking types as a possible way to structure university students' discourse in asynchronous discussion groups and consequently promote their learning. More specifically, the aim of the study is to determine how requiring students to label their contributions by means of De Bono's (1991) thinking hats affects the ongoing critical thinking processes reflected in the discussion. The results suggest that tagging thinking types significantly promotes critical thinking in general and the critical thinking processes during problem identification and problem exploration, in particular. More specifically, it appears that requiring students to reflect on the type of thinking in their contributions stimulates more indepth and focused contributions and, more frequent input of new problem-related information and new ideas for discussion. (Contains 4 tables.)