A greenhouse study with barley (Hordettm disticlton L.) and wheat (Triticum aestivum L.) grown on two mineral soils and fertilized with three levels of 7-yr-old compost combined with four different levels of nitrogen (N) showed that boron (B) toxicity was dependent on the amount of N used in combination with compost. At high rates of compost, symptoms of B toxicity characterized by brown spotting and a burning appearance on older leaf tips, were moderate to severe in both crops. Addition of N decreased the severity of these symptoms; at a high rate of 150 ppm applied N, B toxicity was negligible. The B concentrations of the tissues of the two crops increased with increasing rates of compost and decreased with increasing rates of N in the soil. There was a significant interaction between the rates of compost and applied N. At low rates of N, increased applications of compost resulted in greater concentrations of B. Increasing rates of compost decreased the manganese (Mn) concentration of the boot-stage tissue. 'the tissue Mn concentrations ranged from 44 to 185 ppm and were not the cause of toxicity symptoms noted on the leaves. The N/B ratios of 249-520 were associated with severe to medium B toxicity, whereas ratios of greater than 682 were associated with very few to no B toxicity symptoms.