Purpose: Some EMS systems use resident (RES) physicians to provide on-line medical control (OLMC). Resident inexperience may result in less efficient communication. Objectives: To compare EM faculty physicians (FAC) response to EM senior RES. To determine factors associated with timeefficient OLMC communication. Design: Retrospective cohort for consecutive six months. Setting: A single base-station university hospital staffed by EM FAC (3,300 calls/yr answered by either FAC or RES). Measurements: On-line medical control audio tapes and written records of radio and telephone calls were reviewed. Paramedics (EMT-P) were required to begin OLMC calls with specified information (INFO) (e.g., vital signs, history, treatment). Times were measured using tape deck clock and were reported in mean seconds. CALLTIME = mean time from start to end of physician communication with EMT-P. TOTALTIME = CALLTIME + mean notification time of receiving hospital. Prehospital and Disaster MedicineVol.10, No.4Suppl.https://www.cambridge.org/core/terms. https://doi.