Poor growth of Lupinus angustifolius L. on alkaline soils has been suggested to be due to effects of both high calcium concentrations and high ionic strength in soil solutions on growth. This glasshouse study investigated the effect of calcium supplied as either CaCO3 or CaSO4 to an acid soil on the growth of N-fertilized and N2-fixing plants of L. angustifolius cv. Gungurru, and compared responses of L. angustifolius and Lupinus pilosus Murr., an alkaline-tolerant species, to high ionic strength in high pH solutions. Increasing CaCO3 application increased soil solution pH, and decreased shoot and root growth and chlorophyll concentration in the youngest fully expanded leaflets of both Na-fixing and N-fertilized plants of L. angustifolius. The effect of CaCO3 in decreasing root length was prior to and more pronounced than that on shoot weight and chlorophyll concentration. Adding CaSO4 increased calcium concentration in soil solution by 1.7-6.6 fold and calcium concentration in leaves by 10-30%, but did not markedly decrease the growth of plants grown at any rate of added CaCO3. Increasing pH in nutrient solution from 5 2 to 7.0 decreased shoot weight of L. angustifolius, but slightly increased that of L. pilosus. Plant growth of both L. angustifolius and L. pilosus was slightly decreased as solution ionic strength increased. The effect of high ionic strength was similar whether CaCl2 or KCl was the source of ions. The results suggest that poor growth of L. angustzfolius relative to L. pilosus on some alkaline soils is not caused by excessive calcium or high ionic strength, rather high pH effects on root extension appear to be the major cause of the poor growth.