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Indiangrass [Sorghustrum nutans (L.) Nash] lacks sufficient seedling atrazine [6-chloro-N-ethyl-N’-(l-methylethyl)-1,3,5-triazine-2,4-diamine] tolerance to permit the use of atrazine as a pre-emergence herbicide. The principle objective of this study was to estimate the genetic variability for seedling atrazine tolerance in two indiangrass populations, 'Nebraska 54' and 'Holt', using seed harvested from replicated clones. Seedling survival in soil containing 3 mg kg-1 atrazine was determined in the greenhouse. There was significant genetic variability among half-sib families of both populations for seedling atrazine tolerance. Heritability estimates were greater than 0.50. There was also significant genetic variability among the parent plants of both populations for atrazine tolerance as measured by the change in relative fluorescence (CRF) of leaf disks exposed to atrazine. Atrazine blocks photosynthesis, causing differential fluorescence among plants differing in tolerance, which can be measured with a fluorometer. Correlations of CRF of the parent plants and the seedling atrazine tolerance of their progeny were low (r < 0.3) indicating that fluorescence assay would not be a usable screening procedure. Improving the seedling atrazine tolerance of indiangrass using the greenhouse soil test and conventional breeding methods is possible.