Partially purified samples of the acid phosphatase (EC 3.1.3.2) and of the phytase (EC 3.1.3.8) from A. ficuum were prepared by gel-filtration and ion-exchange dextran chromatography.The pH optimum in o· 02M phthalate buffer of the acid phosphatase was found to be 2·2, while in the same buffer the phytase was found to have at least two optima at pH 2·5 and 5·3, with the suggestion of a third at pH 2·8.The Km value of the acid phosphatase was 1 ·27 x 10-4M with sodium myo-inositol hexakisphosphate as substrate at pH 2· 2. Similarly the Km value of the phytase at pH 2· 5 was 2·44 x 10-sM and at pH 5·3 it was 1·29 x 10-SM.Of a range of inositol hexakisphosphates tested as substrates the order of ease of hydrolysis wasfor the phytase at pH 5·3.The major pentakisphosphate produced by the acid phosphatase at pH 2·2 from both D-chiroand L-chiro-inositol hexakisphosphate was the respective 1,2,3,4,6-pentakisphosphate. In the case of the phytase, at both pH 2·5 and 5·3 the major pentakisphosphate products were the 1,2,3,4,6-and the 1,2,3,5,6-isomers from the D-chiro-and L-chiro-substrates respectively.Neither enzyme was inhibited by 1 mM oxalate, 1 mM citrate, 1 mM EDTA or 1 mM (+ )-tartrate The activity of the acid phosphatase was reduced to 17% and that of the phytase at pH 2·5 to 69% by 1 mM fluoride. The phytase was not inhibited at pH 5·3 by any of the anions tested.