Agent platforms designed for Internet-scale, open networks need scalable and secure location services for agents and services. The location service based on the Fonkey public key distribution infrastructure presented in this paper has been designed and implemented for this purpose. It is scalable in the total number of published identifier–contact address pairs, the number of updates/changes, and the number of agent platforms publishing and requesting contact addresses. This system also supports a signing mechanism to authenticate the publisher of an identifier–contact address pair. Experimental results show that the current implementation based on the Bunshin/Free Pastry overlay network exhibits good scaling behavior.