Botrytis cinerea secreted low levels of a constitutive acid phosphatase into liquid culture when grown in the condition of phosphate starvation or in the presence of high concentrations (4 mM) of organic phosphate esters or inorganic phosphate. During phosphate starvation the overall acid phosphatase activity secreted into the culture fluid was increased up to 80-fold due to the appearance of a second (phosphate-repressible) enzyme form. On native polyacrylamide electrophoresis gels, the constitutive enzyme displayed size heterogeneity, whereas the repressible enzyme was resolved as a discrete band. Both forms of the enzyme reacted with p-nitrophenylphosphate under such conditions, but only the constitutive form was found to hydrolyse β-glycerophosphate. Histochemical staining with these two substrates with the Gomori lead-capture method revealed significant staining of secretory vesicles in the hyphal tip region only in phosphate-starved mycelium with p-nitrophenylphosphate as the substrate. By contrast, vacuolar structures were stained with both substrates under conditions of phosphate starvation as well as abundance of inorganic phosphate. The implications of these observations for the likely exit route of the two acid phosphatase forms are discussed.