This paper is concerned with
calculating centers of regular self-injective rings, particularly those obtained by
completions with respect to rank functions, and those obtained as factor rings of
other regular self-injective rings. Sufficient conditions are developed under which the
completion of a regular ring R has the same center as R. For any regular
self-injective ring R of Type If, it is shown that the center of any factor ring of
R is a factor ring of the center of R. These results are used to distinguish
among the simple regular self-injective rings of Type IIf by their possible
centers.