Two enzymes splitting inorganic pyrophosphate (I and 11) have been investigated in Candida utilis. The results indicate that only enzyme I (no oonsiderable thermoinactivation -10 min, 71 "C -, optimum near pH 2.5, enzyme strongly bound to the cell, high splitting rates in wiwo, derepression under phosphate starvation conditions) is also able to split orthophosphoric monoesters. Thus, the enzyme I is an unspecific acid orthophosphoric monoester phosphohydrolase (E. .C. 3.1.3.2.).