Nature holds numerous viral and bacterial proteins with regions of similarity to myelin basic protein antigenic determinants. Bioinformatic technology, including sequence similarity searches, may allow for the detection of biochemical and biophysical relationships between these peptides. Understanding these relationships is essential to understanding immune-mediated disease and, consequently, may be used to elucidate the etiology of pathological demyelinating diseases such as multiple sclerosis. Studies of experimental autoimmune encephalomyelitis have been used to identify antigenic determinants. We have used these determinants to search available databases of viral and bacterial proteins. Our results indicate numerous viral and bacterial protein segments with probabilistic sequence similarity to myelin basic protein antigenic determinants.