The expression of genes corresponding to twenty four cDNA clones ( Ssci) representing cold induced mRNAs was examined by Northern blot hybridization in potato plantlets treated with cold, NaCl, sorbitol, water and ABA and is illustrated by data representative of the four expression patterns. The response of the genes to cold was examined in two genetically related potato species: a cold tolerant acclimating Solanum sogarandinum and a cold sensitive cultivated Solanum tuberosum, cv. Cisa. The results of Northern blots revealed that only genes corresponding to four of the analyzed clones ( Ssci1, Ssci12, Ssci17 and Ssci20) showed much higher levels of accumulation of the corresponding transcripts during cold treatment in the cold resistant potato as compared with the cold sensitive one. On the other hand, a few other clones ( Ssci3, Ssci4, Ssci6, Ssci13, Ssci21 and Ssci29) showed higher levels of the transcripts accumulation in the cold sensitive potato. The remaining 14 clones showed similar levels of the accumulation of the corresponding transcripts under cold in both potato types. With the exception of Ssci12, the clones were not induced by ABA, NaCl, sorbitol or water treatments. There were no differences in the levels of the corresponding transcripts between the control plantlets and those treated with ABA, NaCl, sorbitol and water. The expression of the clones was not regulated in the day/night cycle; however, the Ssci1 and Ssci2 clones, encoding two different S-adenosyl- l-methionine decarboxylases (SAMDC), were up-regulated at night. The level of induction of the Ssci12 clone, encoding the TAS14 protein (dehydrin), was much higher following treatments with ABA, NaCl and sorbitol than with cold and the gene does not respond to water stress. Higher activity of the genes corresponding to the Ssci1, Ssci12, Ssci17 and Ssci20 clones during cold hardening in the cold resistant potato suggests that their expression is associated with the development of freezing resistance. Among them, the genes corresponding to the Ssci17 and Ssci20 clones are cold acclimating specific ones (cas).