This dissertation was undertaken to address three research objectives: (1) investigating bivariate relationships between search determinants and the amount of information search for prescription and non-prescription drugs, (2) constructing models of external search for prescription and non-prescription drugs, and (3) comparing the differences between consumers' external information search for prescription and non-prescription drugs. A mail survey of 600 randomly selected adults age 45 years and older was implemented to address the research objectives, and 205 useable questionnaires were returned. This research found: " Higher levels of purchase involvement increased the amount of information search using mass media and professional sources for prescription drugs. " There was an inverted-U relationship between subjective knowledge and the amount of consumers' information search using mass media, professional and Internet sources for non-prescription drugs. " Consumers increased their information search efforts using professional sources for prescription drugs when they feel higher levels of threat from diseases. " Perceived benefits of search had positive effects on the amount of external information search using mass media and professional sources for non-prescription drugs. " Younger consumers engaged in more information search using brand Web sites, health-related Web sites, magazine advertising and medical journals / books for prescription drugs than older consumers. " Consumers were more likely to use professional sources and Internet sources to search for information about prescription drugs than non-prescription drugs while consumers were more likely to use mass media and interpersonal sources to learn about non-prescription drugs than prescription drugs. " Consumers' external information search behaviors for prescription and non-prescription drugs were similar in terms of overall information source usage patterns and thought processes leading to information search. The significance of the results is discussed relative to the relevant literature. Theoretical and practical implications are also discussed, followed by suggestions for the future research studies in this emerging area.