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Screening cultivars for aluminum (Al) tolerance is often conducted in acid soils or in complete nutrient solutions. The former method lacks precise measurements of Al, and the second requires high Al concentrations because of precipitation and chelation of the Al and is less representative of the actual environmental stresses to which plants must adapt. These experiments were designed to determine Al tolerance of wheat (Triticum aestivum L. em Thell) and sorghum (Sorghum bicolor L. Moench) using incomplete solutions with very low Al concentrations. Six wheat and five sorghum cultivars were screened for Al tolerance in solution culture with 0 to 10 mu M Al and only Ca, K, Mg, NO3, and Cl in the solutions. Plants were subjected to the solutions for 4 d, and the change in relative root length was measured. Solution Al levels and pH were measured after the termination of the experiments. `Atlas’ 66 and `Stacy’ were the most tolerant wheat cultivars (`Atlas 66’ = `Stacy’ greater than or equal to `Monon’ greater than or equal to `Scout 66’ greater than or equal to `Arthur 71’ = `Oasis’). The wheat cultivars were effectively separated on a genetic response basis at 2 mu M Al. Sorghum cultivars were uniform in their Al tolerance, but did show some separation at 1 mu M Al (SC56 > Tx430 > `Funk GS22DR’ > SC283 = SC599). The pH and Al variations did not account for any of the differences observed, indicating that root length differences were caused by genetic control of response to high Al.