We report an investigation into the relationship between Aspergillus nidulans mutations sltA1 and agaA50, conferring salt sensitivity and arginase deficiency, respectively, and the ability of spores to swell and commence germination. Spores from both mutant strains exhibited uncontrolled swelling at pH 5.5 in the presence of arginine as the nitrogen source. The controlled swelling of spores from a salt tolerant strain under these conditions was disrupted by the Na+/H+ exchange inhibitor amiloride. Swelling in the presence of amiloride was associated with an elevation in the concentration of arginine within the spores of each strain tested. The possible consequences of alterations in the arginine economy of the spore for colony establishment in osmotically challenged habitats are discussed.