Referral services are to be distinguished from reference service, discussed earlier. Referral services do not provide the user with the documents or information actually' needed for his query but refer him to the sources such as secondary publications, information units, professional organisations, research institutes and individual specialists, etc. and tell him where to find them. They utilise directories and files on sources, if necessary, specially created for the purpose. Referral services can function on their own or in cooperation with other services. It is very difficult to measure the effectiveness of such services unless they keep themselves in close touch with their sources and users. Such a task is easier only when referral services offered for the clientele is in a small geographical area.