This paper presents an empirical analysis of the real internal rate of return to the old age insurance (OAI) portion of the old age, survivors, and disability insurance (OASDI) program for worker-only beneficiaries retiring between 1967 and 1970. Section I reviews the analytical background for this study. The issues concern alternative measures of individual equity and the empirical approach to their measurement. The procedures used in five papers on the subject by John Brittain (1972), Colin D. Campbell and Rosemary G. Campbell (1967), Henry Aaron (1974), Yung-Ping Chen and Kwang-wen Chu (1974), and Ubadigbo Okonkwo (1975) are also described. Sections II and III describe the basic model employed and the results. The authors' use of a random sample of longitudinal microdata on actual earnings histories, the feature which distinguishes their approach from previous studies, is also described. The final section compares the authors' results with those of other studies and sets out plans for extension of the analysis. References are included along with an appendix showing detailed tabular results of average internal rates of men and women (1968-1970). (Authors/WL)