In a greenhouse experiment, sorghum was grown in 2 soils watered to capacity when the m.c. reached (a) 90, (b) 50 or (c) 10% of the available water holding capacity, with or without inoculation with Glomus macrocarpus and with P supplied as monocalcium phosphate (MCP) or hydroxylapatite (HA). In a strongly P-fixing soil with MCP as P source, sorghum shoot and root growth was not increased by mycorrhiza. Growth was slightly better in (b) than in (a) and c. 20% lower in (c); the response was similar with and without mycorrhiza. DM production in all treatments was lower with HA as P source. Mycorrhiza increased shoot and root wt. in all water regimes and affected the response to water regime. In a soil with fair P availability, mycorrhiza increased shoot growth and reduced root growth when MCP was used as P source. In both mycorrhizal and nonmycorrhizal plants, shoot growth decreased slightly from (a) to (b) and sharply in (c). Root growth was not influenced by water regime. In spite of weak fungal infection, mycorrhiza had more influence on growth and water consumption than in the P-fixing soil. Where HA was used mycorrhiza increased shoot growth, especially in (a); root growth was weaker and water consumption 17% lower with than without mycorrhiza. In experiments with sorghum and Eupatorium odoratum the favourable effect of mycorrhiza (Glomus macrocarpus) on plant growth was more pronounced in a drier water regime, particularly with restricted P uptake. Mycorrhizal plants were less sensitive to temporary water shortage than non-mycorrhizal plants. It is concluded that under conditions of insufficient soil moisture mycorrhiza can improve the water relations of crops, depending on plant sp. and soil type.