An experimental study was designed to study the effectiveness of Problem Based Learning (PBL) in the context of higher education in an urban-city university in Lima, Peru. In the fall semester of 2004, eleven sections of Chemistry 1 were offered to first year students in the College of Science at this University. In six of these eleven sections students were exposed to PBL; and in the other five sections, to instruction based on lectures mixed with small group activities. There were near 60 students in each section; approximately 660 students participated in the study. The basic measure of the study was a pre and post-test that incorporated questions for each of the levels of Bloom's taxonomy. Students in the PBL sections scored statistically significantly higher in the post-test for the higher order of thinking skill items (analysis-synthesis and evaluation), than students in the non-PBL sections. The latter did better in the lower skill items (knowledge and application). The hypothesis that PBL develops higher order of thinking skills among first year college students, more effectively than other non-PBL approaches, was strongly supported by the data. (Contains 5 tables and 4 endnotes.)