This thesis is an investigation of the willingness of consumers to externally search for information after seeing a prescription medicine in a Direct-to-Consumer Advertising (DTCA) of Prescription Medicines, and from what sources. Through the measurement of external search determinants; prior knowledge, involvement, and attitude towards DTCA, a model for external search initiated by DTCA was developed. Data was collected through a mail questionnaire that exposed 107 respondents to a DTCA for an arthritis drug and asked about their attitudes and behavioral intentions towards the ad. The results show involvement and ad content to be important determinants of external search initiated by a DTCA. The results also show physicians as being the most desirable source of prescription drug information.