It is found that H-HoArg-OH (L-homoarginine), a homologue of arginine, is a strong inhibitor of human bone and liver alkaline phosphatase while it has virtually no effect on intestinal and placental alkaline phosphatases unlike H-HoArg-OH which inhibits intestinal and placental alkaline phosphatases but not the liver and bone enzymes. These four tissues mentioned are the major contributors to the serum alkaline phosphatase. It is also indicated that low levels of the endogenous amino acid H-HoArg-OH are linked to cardiovascular disease.