Purpose: Online information vendors currently offer a variety of additional services; among these are alert services which present requested information on recent publications to registered users. This paper aims to investigate a variety of alert services provided by four online information vendors. Design/methodology/approach: A comparison of the alert services of major online information providers (Ebsco, ProQuest, ScienceDirect, and Scopus) used by the Central Library of Tarbiat Modares University in Iran was undertaken. These alert services were evaluated using a check-list and their structure and service were compared with regard to the quantity and quality of received alerts. The subject area of library and information science was used for the study. Findings: No relative significance was found between the total alerts' relevance and the size of the databases of journal articles. ProQuest was found to have a more reliable alert system and it provided more relevant alert results than the other services. Users should recognise that additional services, such as alert services, are a useful help to their information-seeking behaviour. Library managers should regard alert services as an effective tool for current awareness purposes. However, careful attention should be given to the differences and structures of the services offered. Alert quantity does not necessarily mean good performance. Originality/value: University libraries and information centres pay a lot of money annually to online information providers. Alert systems could reduce the time users spend seeking for information by providing quick access to new information. Therefore, performing a study to investigate the functionality of the alert systems seems appropriate. (Contains 3 tables and 1 figure.)