The Metal-responsive Transcription Factor (MTF-1) serves as an essential regulator of Zn(2+) homeostasis via the activation of metallothionein gene expression. Only a single mtf-1 gene has been identified in any organism investigated previously. We report here the first evidence of the existence of two genes encoding MTF-1 proteins (mtf-1.1 and mtf-1.2). The expression patterns were followed in the liver, kidney, muscle, brain and heart by means of Northern hybridization and reverse transcription coupled polymerase chain reactions (RT-PCR). mtf-1.1 mRNA was detected in all tissues examined, with the highest level in the brain, and the lowest in the kidney and the liver. mtf-1.2 expression was detected exclusively in the brain. Cold shock and Cd(2+) exposure influence the gene expression at the transcriptional level, in a stress-specific manner.