OBJECTIVES: The goal of this paper is to test the leader-follower model in the Argentinean pharmaceutical markets where patent protection does not apply allowing immediate entry. METHODS: It was used a leader-follower model where followers take leader prices to decide their own ones and the leader strategically incorporates followers' behavior in its decision. Two different groups of followers are studied separating the main three from the rest of the market competitors. The data used in this study is based in information published by Pharmaceutical Markets Argentina (PMA) complemented with indicators of needs and chronicity, obtained through interviews with physicians and pharmacologists, as well as the list of chemical entities used in the production of each product, and the nationality of manufactures. RESULTS: From the group of 88 therapeutic classes selected, 56 classes kept the same leader during the period 1988-1995, although just in nine of those cases the first entrant remains as market leader. The cases where market leader remains the same during the sample period but they were not necessarily the first entrants are defined as loose leadership markets, while cases of strict leadership are those where first entrants remained as market leaders during the sample period. CONCLUSION: The leader-follower hypothesis is checked and supported by the data, mirroring the results obtained under a patent regime. In addition, the lack of patents also raises the question of difference in behavior among followers. Therefore, two differentiated groups of followers are studied separating the main three from the rest of the market competitors.