The investigation of functional systems controlling organogenesis and maturation of potato tubers is undoubtedly of interest. These studies are necessary for a better understanding of plant improved ecological resistance and tolerance to pathogens during their transition to dormancy and the resumption of active growth and development. We realize now that tuber biochemical composition change during their development. Monosaccharide polymerization and starch accumulation, amino acid synthesis and protein accumulation, and deposition of fatty acids, macro- and micronutrients are largely studied [1‐6]. However, the establishment of protective compound pools, antioxidants and some low-molecular-weight substances, during tuber development remain to be properly studied. These compounds determine tuber resistance to diseases during maturation and subsequent storage in autumn and winter. Physiological and biochemical characteristics of tuber development of newly introduced potato cultivars are important for practical application. They are useful for the assessment of optimum tuber state before their harvesting, which ensures the maintenance of their viability and nutritional quality during a storage period. In this connection, the objective of this study was to follow the accumulation of starch, soluble carbohydrates, chlorogenic acid, and flavonoids during tuber development in three potato cultivars differing in earliness and rhythms of tuber physiological maturation. Experiments were performed in 2002 and 2003 in the experimental plot of the Laboratory of Plant Physiology and Biochemistry of Tsitsin Main Botanical Garden of the Russian Academy of Sciences. We used three potato cultivars differing in ripeness time: cv. Zhukovskii rannii (early ripeness), cv. Golubisna (moderate ripeness), and cv. Nikulinskii (moderate-late ripeness). In 2002 and 2003, seed tubers were planted on May 8 and May 20, respectively. Plants were repeatedly and sufficiently watered and fertilized with nitrogen, phosphorus, and potassium. However, climatic conditions were very unfavorable. In 2002, summer was very hot and droughty; whereas in 2003, the weather was frequently excessively wet and cold. Tables 1 and 2 present the average date for the two years. Tubers were sampled three times with the intervals of ten days. Chlorogenic acid was determined by the method of Zuker and Ahrens [7]. Flavonoids were measured as described by Harborne [8]. Monosaccharides and total soluble carbohydrates were estimated as described in [9]. Starch content was determined in the tuber homogenate by the method elaborated in our laboratory. Taking into account an uneven distribution of all tested compounds within tubers and a great diversity in tuber biochemical composition, we calculated data per the total weight of all tubers from a single plant. All analyses were performed in two or three replicates with three recordings each. Statistical treatment was performed according to [10].