Phosphatase enzymes regulate organic phosphorus (P) turnover in soil, but a clear understanding remains elusive. To investigate this, phosphomonoesterase and phosphodiesterase activities were determined by using para-nitrophenol (pNP) analogue substrates in a range of temperate pasture soils from England and Wales. Substrate-induced phosphatase activity ranged between 2.62 and 12.19 micromol pNP g-1 soil h-1 for phosphomonoesterase and between 0.25 and 2.24 micromol pNP g-1 soil h-1 for phosphodiesterase. Activities were correlated strongly with soil pH and labile organic P extracted in sodium bicarbonate, although the relationships differed markedly for the two enzymes. Acidic soils contained high phosphomonoesterase activity, low phosphodiesterase activity, and high concentrations of labile organic P, whereas the reverse was true in more neutral soils. As most of the organic P inputs to soil are phosphate diesters, it therefore seems likely that phosphodiesterase activity regulates labile organic P turnover in pasture soils. The low phosphodiesterase activity in acidic soils may be linked to the dominance of fungi or an effect of sorption on the enzyme. These results suggest that greater emphasis should be placed on understanding the role of phosphodiesterase activity in the cycling of soil organic P.