Sucrose and starch concentration, sucrose phosphate synthase (SPS) activity in leaves, and long distance transport were studied in maize seedlings treated with moderate chilling (14 °C/12 °C -day/night).Two inbred lines were tested: chilling-tolerant KW1074 and chilling-sensitive CM109. Seedlings were grown in phytotrone on water nutrient tmtil the 4-th leaf appearance. The estimations were done on fully developed 2-nd leaf.Six days after the temperature was lowered, leaves of line KW 1074 plants contained 5-fold more sucrose and starch than the control ones. The same treatment of CM 109 seedlings resulted in accumulation of sucrose and starch by 2-fold and 8.5-fold, respectively.As the result of chilling-treatment, 14C assimilation rate (Pa), transport speed in the leaf blade (TS1) and along the plant (TSm) decreased by about 50 % in both lines. On the other hand, time necessary for radiolabel movement into the phloem loading region (AT) increased strongly, especially in chilling-sensitive line CM 109. It was also noted, that the radioactivity exported from leaves (RI) and imported by roots (Rm) decreased in line CM 109, and increased slightly in line KW 1074.The activity of SPS extracted from leaves of both lines decreased by about 3.3 when temperature was lowered form 30°C to 10°C. There was no effect of 6 day treatment of chilling on SPS activity.Changes in sucrose and starch concentration, SPS activity as well as differences in transport parameters observed in KW1074 and CM109 seedlings at moderate low temperatures are discussed in terms of mechanism of maize chillingsensitivity.List of abbreviations: Pa-14CO2 assimilation rate;AT -time of radioactivity appearance in the loading region; R 1 -radioactivity of leaves near the feeding area, Rm -radioactivity of mesocotyl; TSI -speed of translocation in the leaf blade; TS m -speed of translocation between leaf and mesocotyl, PCMBS p-chloromercuribenzen esulphonic acid, SPS -sucrose phosphate synthase