Some of the major studies by the proponents of the Derivational Theory of Complexity are reviewed in this paper, and the results of a study to determine the adequacy of the theory as an account of message processing difficulty are included. The subjects for the study were students selected from five sections of the introductory communication class at Michigan State University during the spring quarter of 1973. Despite the failure of this study to produce statistically significant results, the research demonstrates the existence of social class correlates of language processing and suggests the need for the inclusion of socioeconomic variables in psycholinguistic research. (RB)