Information on the number and types of communication activities (including travel) engaged in over a period of four consecutive days, at two points in time about six months apart, was collected from 91 respondents in the context of the introduction of a community network to the city of Davis, California. Three major types of communication were measured: personal meetings (and in a separate but related measure, trips), transfer of an information object (in-house documents, regular mail, and express or overnight mail), and electronic (phone, fax, and e-mail). A system of structural equations was developed and estimated, expressing the number of instances of each type of communication at time 2 as a function of: the number of instances of each type at time 1, the elapsed time between measurements, and exogenous sociodemographic variables. All "own" lagged effects (that is, the effect of one communication type in wave 1 on the same type of communication in wave 2) were found to be positive and (except for information object delivery) highly significant. The "elapsed time" variable was always positive and (except for personal meetings and, in one model, information object delivery) significant; these effects indicate net generation of communication activities over time. Significant "cross" lagged effects (that is, the effect of one communication type in wave 1 on a different type in wave 2) were mostly positive, indicating the presence of some complementarity effects across modes. However, relationships specifically between electronic forms of communication and personal meetings or trips were not significant in either direction for the final models. Several exogenous variables were significant in logical ways.