The Mpv17l protein has two isoforms, M-LPL and M-LPS, which both regulate the production of reactive oxygen species (ROS) and protect against mitochondrial oxidative stress and apoptosis. M-LPL is ubiquitously expressed, while M-LPS is expressed mostly in the kidney of aged animals. We identified a variety of transcripts of the Mpv17l gene that could encode novel isoforms by mapping expressed sequence tags on the mouse M-LP genomic locus. We analysed the expression and evolutionary conservation of a novel Mpv17l transcript (mpv17l-002) that is predicted to encode a new protein, termed M-LP2. The isoform M-LP2 has the full length of M-LPS plus six amino acids at the end of its amino terminus, which could be encoded by an alternative 5'-flanking sequence. We show that the mRNA of M-LP2 has a different pattern of expression than the mRNA of M-LPS, and sequences of both transcripts are conserved in the rodent genome; however, neither of these isoforms is detected in the human genome. These observations suggest that the functions of certain M-LP isoforms are tissue- and species-specific, implying that their potential involvement in ROS metabolism may be redundant or may be complemented by other members of the Mpv17 family.