Summary Acid phosphatase activity associated with the root and in the rhizosphere of rape (Brassica napus) L., wheat (Triticum aestivum L.) and onion (Alliutn cepa L.) plants was investigated in the presence or absence of vesicular‐arbuscular mycorrhizal fungi. The plants were inoculated singly with three different species of Glomus, or were left uninfected, and were grown in sand with little available phosphorus. Root and rhizosphere levels of phosphatase activity were higher for plants infected with G. geosporum (Nicol. & Gerd.) Gerd. & Trappe and G. mosseae (Nicol & Gerd.) Gerd. & Trappe compared with control plants. Infection with G. monosporum Gerd. & Trappe did not result in a similar increase in phosphatase activity but significant increases in plant growth nevertheless occurred. Further experiments, using wheat only, showed that increases in phosphatase activity induced by infection by G. geosporum or G. mosseae became apparent between 25 and 51 d after sowing.

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