The present study explores the factors that determine doctors’ perceptions of the usefulness of online professional services and the latter’s influence on their purchase intention. The study’s conceptualization is based on the Technology Acceptance Model and the incorporation of professionals’ individual differences as well as the nature of the online service. On this basis, a theoretical framework is developed and empirically tested using data collected from 100 physicians through personal interviewing. During the interviews each of the physicians was asked to provide information on the study’s variables for two different types of innovative online services (commercial or educational). The results indicate that perceived usefulness is positively related to four major variables: perceived ease of use, social influences, individual differences (as described by the physician’s level of education, work status and self-efficacy) and the nature of the service. Finally, in agreement with former studies, the relationship between perceived usefulness and physicians’ purchase intention was also found positive and significant. Based on the study’s results, important implications for managers and suggestions for further academic research are presented.