Abstract: An electronic locking system comprises an electronic lock for an external door of a building, and a plurality of electronic locks associated respectively with internal doors of a building accessed via the external door. The lock of each internal door includes means for storing at least one unique lock combination code and the lock of the external door including means for storing a plurality of the unique lock combination codes of a plurality of the internal doors and/or a common combination code. Key cards operate the locks. A first control means operable if the number of internal doors accessed through the external door is less than a predetermined number designates a unique lock combination for each internal door and encodes the associated key card with the unique lock combination. A second control means operable if the number of internal doors exceeds the predetermined number provides an overload signal recognizable by an operator.