The invention relates to a method, an exchange, a telecommunication system and a mobile station for providing a temporary selective national roaming at predetermined network operation conditions, e.g. at network overload in a mobile radio communication system. A first switching means (MSC/VLR) of a home network (HPLMN) performs a negotiation with a second switching means (MSC/VLR') of another network (VPLMN) which has free capacity to handle mobile stations (MS1-MS4) of the first network (HPLMN) which cannot be handled by said first network (HPLMN) during e.g. an overload condition occuring therein. When e.g. the overload condition occurs, a request message (RM) is first sent to the second switching means (MSC/VLR') in order to enquire whether the second network (VPLMN) has enough free capacity to take over mobile stations (MS1-MS4) from the first network (HPLMN). Thus, it can be ensured that mobile stations (MS1-MS4) of the first network (HPLMN) do not cause an overload condition in the second network (VPLMN) when they have been registered in the second network (VPLMN) and receive a service therein.