Noting that little theory has been developed to explain how and why organizations choose to manage public relations, this paper argues that theorists cannot improve the practice of public relations until they can explain what public relations is and what it contributes to the functions of an organization. The paper addresses that issue by continuing a research program begun in a 1976 issue of "Journalism Monographs," in which the relationship between two kinds of organizations, the "problem solving" and the "fatalistic," and two kinds of public relations, diachronic and synchronic, were analyzed. The paper enlarges that dichotomous theory to include four models of public relations: (1) the press agency/publicity, (2) public information, (3) two-way asymmetric, and (4) two-way symmetric models. It then develops two typologies of organizations based upon their product/service and political/regulatory environments to explain the types of organizations that use each of the models. The paper conceptualizes the four models based upon public relations history, then presents four indices to measure the models, along with the results of a reliability analysis of the indices. In conclusion, the paper presents the results of case studies of 16 organizations in which interviewers measured the public relations models and related them to organizations and environmental variables. (The questionnaire used in the case studies is appended.) (Author/FL)