For the purpose of investigating the genetic basis of antigenic variation in Trypanosoma brucei, we have analyzed the structure of the genome surrounding the gene coding for one T. brucei variable antigen (IL Tat 1.2) in several T. brucei clones expressing this and other variable antigens. In each case there are two copies of the gene. We found no evidence of an extra copy associated with the expression of this gene. Differences were found between the two copies in a single clone, and between the copies in different clones. The differences could be explained by insertion and deletion of various lengths of DNA in a region beyond the C-terminal end of the gene. Differences in genomic structure were found even between clones expressing the same antigen, whether IL Tat 1.2 or another. Thus, no feature of the rearrangements observed can be correlated with the expression of a particular antigen.