RNA editing post-transcriptionally modifies several mRNAs from the maxicircle of kinetoplastid parasites by addition and removal of uridine residues. We report here that maxicircle CR5 transcripts of Trypanosoma brucei are edited in two domains separated by an eight nucleotide sequence that remains unedited. The large 5' domain is edited to a consensus sequence while the smaller 3' domain is edited to multiple final sequences. In all, 205-217 Us are inserted and 13-16 encoded uridines are deleted from the CR5 mRNA, producing a mature transcript 75-80% larger than the unedited transcript. The edited RNAs predict small, highly hydrophobic proteins. The carboxy terminal 15-30% of these predicted proteins have multiple different amino acid sequences as a result of the variable edited 3' mRNA sequence, but these fall into two families of sequence. Limited amino acid sequence and hydrophobicity profile similarities suggest that the protein encoded by edited CR5 mRNA may be a subunit of NADH dehydrogenase.