[en] Alternan, which consists of alternating alpha(1 - 3)/alpha (1 - 6)-linked glucosyl residues, was produced in potato tubers by expressing a mature alternansucrase (Asr) gene from Leuconostoc mesenteroides NRRL B-1355 in potato. Detection of alternan was performed by enzyme-linked immunosorbent assay in tuber juices, revealing a concentration between 0.3 and 1.2 mg g–1 fresh wt. The Asr transcript levels correlated well with alternan accumulation in tuber juices. It appeared that the expression of sucrose-regulated starch- synthesizing genes (ADP-glucose pyrophosphorylase subunit S and granule-bound starch synthase I) was down-regulated. Despite this, the physico- chemical properties of the transgenic starches were unaltered. These results are compared to those obtained with other transgenic potato plants producing mutan [alpha (1 - 3)-linked glucosyl residues and dextran [alpha (1 - 6)-linked glucosyl residues].