A study examined the relationships among source diversity, medium reliance, and nominal issue diversity. Source diversity is defined as the number of categories or classes of sources, and in the study nominal diversity within media (newspapers, television and magazines) was examined. Medium reliance is defined as the perceived usefulness of a given medium for information about issues, while nominal issue diversity is the number of categories or classes of issues considered salient by an individual. A random sample of 223 graduate and undergraduate students at the University of Florida were interviewed. Results suggest positive associations between issue diversity and the following: newspaper diversity, magazine diversity, newspaper reliance and magazine reliance. Television diversity--measured as the number of channels ordinarily watched--was not found to be related to issue diversity. Similar patterns were found between medium reliance and issue diversity. Reliance on magazines and newspapers, but not radio and television, is related to nominal issue diversity. Findings also suggest that media diversity, in combination with motivation, is related to issue domain differentiation. These findings, when integrated with those from previous studies, represent the beginning of a model of issue domain structure and the antecedents of this structure. (A list of 67 sources is provided.) (NKA)