Potato (Solanum tuberosum L. cv Superior) microtubers were formed in vitro and the levels of patatin and its mRNA in microtubers were compared at different stages of development by SDS-PAGE and Northern hybridization. The results showed that potato microbubers also contained approximately 40 KD protein as the major soluble protein like field-grown potators. The amount of patatin gradually increased during development of microtubers, reaching the maximal level at the 60th day of development. In contrast, patatin did not appear to accumulate either in leaves and steams of potato plants bearing microtubers. On the other hand, the level of patatin mRNA during development of microtubers gradually increased for up to 30th day and decreased slightly thereafter. Large amount of starch was also found in potato microtubers, leaves as well as stems of potato plants bearing microtubers. The significant difference observed in the level of patatin mRNA synthesis at various developmental stages suggest that the expression of the patatin gene is developmentally regulated at the transcriptional level.