1. Introduction; 2. Institutional contextual framework; 3. The contextual framework of the course; 3.1 Course population; 3.2 Objectives and contents; 3.2 Learning activities; 3.3 Teaching team; 3.4 Technological platform; 3.5 Evaluation of students' learning; 4. Use of PBL in the online course; 5. Method for the study of peer interaction; 5.1 Sample; 5.2 Instruments; 5.3 Procedure; 6. Results and discussion; 6.1 Trends of thought: Levels of the posted messages in electronic forums; 6.2 Efficiency in the study of the problem: Focus on PBL within the general discussion; 6.3 Level of mastery of the PBL technique: Changes in the use of PBL throughout time; 6.4 Effectiveness of PBL: Contributions of students' collaborative learning; 6.5 Closing statement; 7. Author's note; 8. References