L-Homoarginine is an uncompetitive and organ-specific inhibitor of alkaline phosphatases. This non-essential amino acid inhibits human bone and liver alkaline phosphatases but has no effect on placental or intestinal isoenzymes. In vitro, L-homoarginine inhibits [3H]thymidine uptake by mouse myeloma MOPC 104E cells and inhibits proliferation of C3H/He mouse osteosarcoma cells. Pre-treatment with L-homoarginine delays in vivo tumor growth in a murine C3H/He osteosarcoma model. It also inhibits high-protein diet-induced pancreatic growth and enzyme secretion in bile-pancreatic juice-diverted rats, a model for the induction of pancreatic enzyme secretion with hypercholecystokininemia.