A longitudinal study (1961-1965) was planned to obtain information on the pervasiveness of personal influence with respect to decisions to join formal voluntary associations; examine the characteristics of opinion leaders and the individuals they influence; discover the differential patterns of joiners' exposure to mass communicated messages about the organization; and study the relative importance of social interaction in decisions to participate. The questions administered were part of an interview schedule designed in connection with the Nebraska Adult Interests Study. Of the 1500 interviewed (in 1969) 1/3 were randomly selected (stratifying for sex and county of residence). The original sample of 1500 adults which was selected by using area probability techniques, constituted a representative cross-section of the total population of Nebraska between 21 and 69 years of age. Although people learned about organizations through personal letters of invitation and mass media (newletters, brochures, and newspaper advertisements and articles), the largest proportion of members (77%) came to know about groups through conversations with others. (NL)