The contemporary information-seeking environment is marked by the presence of more information sources than perhaps ever before. Moreover, in the context of health information, evidence suggests that information seekers utilize multiple sources—such as health care providers, print media, and online support groups—in the process of acquiring information. Two studies were conducted to investigate the role of information sources in the health information-seeking process and test Ruppel and Rains’s (2012) extension of channel complementarity theory. Four complementarity characteristics of sources, which are argued to serve as a basis for source use during information seeking, were examined: access to medical expertise, tailorability, anonymity, and convenience. Taken together, the results from both studies offer some evidence that sources are used systematically during health information seeking based on each of the four complementarity characteristics.