One crop of clover followed by three crops of ryegrass were infected with several mycorrhizal fungi and grown in sterilized soil which had received soluble phosphate or Nauru rock phosphate. Plant growth responses to mycorrhizal infection were larger in later crops. Glomus tenuis was successfully introduced into soil already infested with the indigenous mycorrhizal fungi, and was the most efficient fungus used at stimulating phosphate uptake. In all four crops, Nauru rock phosphate was available to mycorrhizal plants but unavailable to non-mycorrhizal plants. Plants infected with G. tenuis and the indigenous mycorrhizal fungi recovered 10-27% of the phosphate fertilizer applied to the soil while non-mycorrhizal plants recovered only 0.4-13%.