The characteristics of nonspecific alkaline phosphatase, (APase, EC 3.1.3.1.) measured asβ-glycerophosphatase (GPase, EC 3.1.3.1.), inorganic pyrophosphatase (PPiase, EC 3.6.1.1.) and adenosine triphosphatase (ATPase, EC 3.6.1.3.) were studied in detail of butanol extracts prepared from rat molar cementum.All enzyme activities showed nearly identical sensitivities to heat inactivation and to L-p-bromotetramisole and levamisole, which caused nearly complete inhibition. About 10–15% of the ATPase activity was insensitive to L-p-bromotetramisole and levamisole. The data are consistent with the concept that GPase, PPiase and ATPase activities of cementum to a major part stem from one enzyme, namely nonspecific alkaline phosphatase.This study was supported by grants from the Anna Ahrenberg foundation, from Magnus Bergwall scientific foundation and from Wilhelm and Martina Lundgren scientific foundation.The author is grateful for the technical assistance given by Ms Elisabeth Granström and for the typing of the manuscript by Ms Ingrid Lundberg.