Previous studies in our laboratory both in pine needles and potato leaves have shown evidence of an increase in 18: 2 (linoleate) in the purified plasma membrane fraction during cold acclimation. This increase was reversible on deacclimation, thereby suggesting a link between the accumulation of 18: 2 and acquisition of freezing tolerance. These studies suggest that the activity of specific desaturases may be modulated during cold acclimation. This study was aimed at studying the possible involvement of stearoyl-ACP desaturase (delta9) in potato cold acclimation response. Our approach was to study the induction of delta9 desaturase at the transcript level by using potato delta9 desaturase gene specific primers and reverse transcriptase. For this purpose, mRNA from S. tuberosum (cold sensitive, unable to acclimate) and S. commersonii (cold tolerant, able to cold acclimate) was extracted before and after acclimation. Sequence analysis confirmed that the amplified band was delta9 desaturase. Our results show that there is an increase in delta9 desaturase gene transcripts during cold acclimation and that this increase is associated with the cold acclimation response in potato. These results together with previous reports on the increase in 18: 2 in the plasma membrane during cold acclimation give more evidence toward the involvement of stearoyl-ACP desaturase (delta9) in the potato cold response.