This paper proposes and tests a model using two dimensions of interactivity (machine and person) to predict consumers' intentions to purchase online. Analysis of the results of an online survey of 1,744 respondents revealed that machine interactivity is positively associated with online purchase intentions through its influence on physical telepresence, attitudes, perceived behavioral control and trust. Person interactivity is positively associated with online purchase intentions through its influence on social telepresence, subjective norms, perceived behavioral control and trust. This paper also compares the relative influence of machine interactivity and person interactivity on intention to purchase online. Implications of the results are discussed to provide guidance for future research and business recommendations to marketers.