This paper reports on the development of an online union catalog of serials using OCLC by the Central New York Library Resources Council. The project, now in the third of four years, is converting from a hard copy union catalog of serials to an online catalog that will have the important advantage of immediate update. Using the OCLC interlibrary loan sybsystem, the inquiring library may look at a display of library holdings and find up to five locations for a given serial--30 of the 45 libraries in the CNY system currently have OCLC capability. The final year of the project will be used to complete the catalog, complete the transition from manual to online operation, and gain user acceptance. A users manual furnishes instruction on reading bibliographic entries, preparation of serials requests, and submission of change information. A directory of participating libraries is included. (RAA)