The effects of para-fluorophenylalanine (p-FPA) and azetidine-2-carboxylic acid (AZ) on acid phosphatase and peroxidase activity, and on L-leucine incorporation, in root segments of Triticum aestivum L. cv. Fenman and Vigna radial a (L.) Wilczek, were studied. Incubation with 50 mmol−3 AZ significantly reduced phosphatase and peroxidase activities in wheat roots, but with 20 mol m−3p-FPA, only the peroxidase activity was reduced. In mung bean roots, phosphatase activity was inhibited by both AZ and p-FPA. Effects of the ortho- and meta- isomers of FPA on wheat root phosphatase and peroxidase, and on mung bean phosphatase, were also examined. Leucine uptake and incorporation were not inhibited by 5 h pre-incubation with either p-FPA or AZ, but were inhibited after 24 h of pre-incubation. The results support the view that, in the shorter term, the analogues inhibit enzyme activity by becoming incorporated to produce non-functional protein and, in the longer term, metabolism is further affected by inhibition of protein synthesis.