Cold acclimation of rainbow trout cells is considered to be mediated by alterations in the mRNAs and proteins present in cold-treated cells. A subtracted cDNA library from cold-treated rainbow trout RTG-2 cells was constructed and screened to isolate cDNA induced in the cold-treated cells in order to elucidate which genes are induced by cold acclimation. A set of cDNA clones encoding three members of ferritin H isoforms was isolated as cold- inducible genes. Northern blot analysis and nuclear run-on transcription assay showed that the transcription and accumulation of the ferritin H isoforms mRNA were enhanced by cold acclimation. Furthermore, the ferritin level in the trout cells increased on cold acclimation in response to a temperature shift from 22 °C to 4 °C. When the trout cells were subjected to 4 °C under the condition of a decreased ferritin H level obtained by the addition of an antisense oligonucleotide, cell growth was apparently inhibited. These findings indicate an association between the induction of ferritin H and cellular mechanisms during cold acclimation of trout cells.