Starches isolated from kernels of two maize (Zea mays L.) inbreds and their F1 progeny, grown after four planting dates, were evaluated for differences in thermal properties. Differential scanning calorimetry (DSC) was used to compare onset (To) and peak (Tp) temperature, range (Rn), and total enthalpy ((Delta)H) values of gelatinization. Amylose content (%AM) of samples was determined colorimetrically, and image analysis was used to determine average diameters of granules. Significant (P less than or equal to 0.05) increases for Tp and (Delta)H were observed with later planting dates. Significant genotypic differences also were seen for To, Tp, and (Delta)H. Later planting dates had no effect on %AM or starch granule size. Genotypes ranked similarly for %AM across each environment, and no differences were observed for average granule diameter. The presence of environmental effects on thermal properties of the starch suggests that if small differences (1-2 C or less than 0.2-0.3 cal/g) are to be identified among nonmutant genotypes, growing conditions may need to be controlled.