Analysis of the sequence of the mitochondrial cyt b gene of Teratocephalus lirellus revealed multiple frame shift events. As these sites coincided with homopolymeric tracks, sequencing was repeated and chromatograms were screened for poorly resolved peaks. No evidence for sequencing errors was found. We therefore reverse transcribed mRNA, using M-MLV reverse transcriptase and two primers for strongly conserved regions located anteriorly (CbF1: >5′-GTTTTGGAATGTTGGAAGGCTTTTAGG-3′) and posteriorly (CbR1: <5′-CCCAGATATCACCATAGCCAAATAGACG-3′) in the gene. The cDNA product was PCR amplified and sequenced, and compared with the gDNA sequences. This revealed insertions of a single U in eight sites in the mRNA sequence (Fig. 1).