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Abstract  Field-grown maize hybrids were assessed for variability in 137Cs accumulation in vegetative parts of young and mature maize shoots and grains during 2 years with contrasting climatic conditions. Trials were carried out at different sites in the Tula region of Russia, which is characterized by a highly homogenous soil classified as Luvic Chernozem according to FAO/UNESCO, and average contamination levels of about 509–564 Bq 137Cs kg−1 soil. In the first year, 19 hybrids were tested. The two hybrids with the highest and the two with the lowest 137Cs concentration ratios (C r) were also tested in the second year, together with another 11 hybrids. All samples were additionally assessed for their potassium content. In both investigation periods 137Cs accumulation in vegetative shoots and grains was found to vary up to more than twofold between hybrids. However, C r values of those hybrids that showed a relatively low 137Cs accumulation in the first year were not necessarily low in the second year, and the ratio between the 137Cs C r of low- and high-accumulating hybrids was much smaller than in the year before. In both vegetative shoots and grains the variance caused by the different years was larger than the genotypic variance, thus indicating the limits of genotype selection for this trait. Significant correlations were determined between the 40K and 137Cs C r values in the same tissue, but for one hybrid indications for uncoupling of the two traits were found. Average Cs/K ratios in young shoots, mature shoots and grains were 0.06, 0.05 and 0.02, respectively, indicating tissue- and stage-specific regulation of accumulation within each plant. The findings are discussed with respect to new approaches towards a better understanding of 137Cs accumulation and its potential reduction in plants. [ABSTRACT FROM AUTHOR]