This contingency study was undertaken to increase understanding of the way in which management support and communication characteristics influence teleworkers' use of communication media. Complexity of communication tasks, communication urgency, and perceived reliability of a medium comprise variables of communication characteristics. These variables represent theoretical dimensions of media richness: perceived task requirement, perceived media characteristics, and attitude toward communication media. Information richness and social influeuce provided the theoretical basis of this study. The study focused on two general-purpose communication media, e-mail and the telephone, and examined how the above factors are used to determine the choice of media. Research data were collected from the formal telework program operated by Fujitsu Kyushu Communication Systems Limited (QCS) in Japan. We differentiate our study from previous studies of media choice by focusing on remotely distributed teleworkers, using clearly defined work groups that permit investigation of collective behaviors, and analyzing data captured during actual use of communication media. Analysis of data indicates that factors of communication characteristics, especially communication urgency and perceived reliability of a communication medium, do influence the media use of teleworkers. Management support, as a direct social influence as well as a moderating force that overcomes the constraint of media richness, greatly improved the adoption and effective use of e-mail