Consumer health information is increasingly available online, but this vast amount of information is not necessarily accessible to general consumers. To design effective health information websites, it is critically important to gain an in-depth understanding of how consumers search for health information in these systems. This study is an attempt to explore consumer health information searching behavior in web-based health information spaces by observing their search behaviors in MedlinePlus. Nineteen undergraduate students accomplished three search tasks in MedlinePlus. The participants used both searching and browsing as interaction strategies. This paper reports on the findings of their searching behaviors, particularly query construction, query reformulation, and access to results; and their browsing behaviors, particularly access to different resources, health topics, and related topics. Furthermore, we examined if the number of concepts involved in search tasks had any impact on search behaviors.