Communication problems among healthcare professionals are known to adversely affect patient care. Web-based healthcare messaging systems (WMS) are seen as a means to improve communication. However, power imbalances among healthcare professionals may affect their communication and WMS use. In this study, we aim to understand how power relations affect WMS usage patterns. The hypotheses are tested through content analysis of over 70,000 WMS messages exchanged through a hospital WMS. We find that powerful parties (physicians) send a greater proportion of conflict resolution messages to weaker parties (administrative staff members and nurses) by WMS than vice versa. Weaker parties send higher proportion of coordination messages to physicians than vice versa. Hospital staff members send higher proportion of relationship development messages to colleagues as compared to other parties. Juniority of physicians is positively related to the number of information gathering messages from nurses. The expected contributions and remaining research plan are outlined.