An acid phosphatase from Trichoderma harzianum was purified in a single step using a phenyl-Sepharose chromatography column. A typical procedure showed 22-fold purification with 56% yield. The purified enzyme showed as a single band on SDS-PAGE with an apparent molecular weight of 57.8 kDa. The pH optimum was 4.8 and maximum activity was obtained at 55A degrees C. The enzyme retained 60% of its activity after incubation at 55A degrees C for 60 min. The K (m) and V (max) values for p-nitrophenyl phosphate (p-NPP) as a substrate were 165 nM and 237 nM min(-1), respectively. The enzyme was partially inhibited by inorganic phosphate and strongly inhibited by tungstate. Broad substrate specificity was observed with significant activities for p-NPP, ATP, ADP, AMP, fructose 6-phosphate, glucose 1-phosphate and phenyl phosphate.