The effect of the zinc (Zn) nutritional status on the rate of phytosiderophore release was studied in three wild grass species (Hordeum murinum, Agropyron orientale, and Secale cereale) grown in nutrient solution under controlled environmental conditions. These wild grasses are highly ''Zn-efficient'' and grow well on severely Zn-deficient calcareous soils in Turkey (DTPA-extractable Zn was 0.12 mg/kg soil and CaCO3 was 37%). In all wild grasses studied, Zn deficiency reduced shoot growth but had no effect on root growth. Low amounts of phytosiderophores were released from roots of all wild grasses adequately supplied with Zn. In plants grown without Zn, release of phytosiderophores progressively increased with the onset of visual Zn deficiency symptoms, such as inhibition of shoot elongation and appearance of chlorotic and necrotic patches on leaves. Compared to Zn-sufficient plants, phytosiderophore release increased 18-20-fold in deficient plants. HPLC analysis of root exudates showed that the dominating phytosiderophore in Zn-deficient Agropyron and Hordeum was 3-epi-hydro-xymugineic acid (epi-HMA) and was 3-hydroxy-mugineic acid (HMA) in Secale. Besides HMA, epi-HMA and mugineic acid (MA) were also detected in exudates of Zn-deficient Secale. The results indicate the importance of phytosiderophores in adaptation of wild grasses to Zn-deficient calcareous soils. Phytosiderophores might enhance mobilization of Zn from sparingly soluble Zn pools and from adsorption sites, both in the rhizosphere and within the plants.