Ecotourism presents developing countries with growing opportunities for attracting foreign exchange and enhancing economic growth, but also raises some pressing management challenges for national parks and other protected areas. This paper presents a framework for analyzing the impacts of increasing user fees on visitation at national parks in Costa Rica. Data are collected at three national parks using a contingent behavior methodology designed to elicit information on foreign tourists' park visitation behavior at alternative entrance fee levels. This methodology employs surveys of subjects responding to hypothetical scenarios involving various pricing and visitation options. Park visitation demand functions and own-price, cross-price, and income elasticities are estimated. Based on these estimates, revenue-maximizing fee levels are calculated and the implications of applying differential pricing principles to park management are discussed. The results suggest important conclusions for national park user fee policies, particularly in developing countries.