Previous research has indicated that instructor immediacy is associated with learning outcomes, satisfaction, and motivation. However, few researchers have examined instructor immediacy in the context of online learning. This study is the first large experiment (n = 433) to empirically investigate the effects of instructor immediacy behaviors (high versus low) and online delivery modality (audio versus video) on participant perceptions of instructor immediacy and social presence. Results demonstrated that participants assigned to the high-immediacy sessions indicated significantly higher perception of instructor immediacy and social presence than participants assigned to the low-immediacy sessions. Findings also established a strong correlation between participants' perception of instructor immediacy behaviors and their perception of the instructor's social presence. (Contains 4 tables and 3 figures.)