Our analysis of idiotypic dominance suggests that 3 elements play an important role. The first is the genetic material that encodes the dominant idiotype. As dominant idiotypes appear to reflect germ-line-encoded sequences, one can not express a particular idiotype unless that sequence is present in the germ line. The germ-line-encoded sequences, in turn, would, I predict, be specific for commonly encountered or former environmental pathogens. The second element is the environmental antigens themselves. These antigens will induce the production of idiotype, and will prime idiotype-bearing B cells, such that idiotypic dominance emerges. In the absence of such influences, the pattern of idiotypic expression appears to differ. The third influence is regulatory. My own studies have shown that idiotype found in normal serum plays an important role in the maturation and/or function of one such cell, an idiotype-specific helper T cell. It is my working hypothesis that such cells play several roles in idiotypic dominance, but that this is the least of their important roles. Rather, such cells, being specific for idiotopes associated with antibodies specific for environmentally encountered pathogens, would be important in the priming and rapid reactivation of B cells bearing such idiotopes. As such, they speak to the basic role of the immune system, the protection of the organism from infection.