EGON 
                He's right to worry, Peter. The Necronomicon's 
                spells are like sonic "keys" that can open 
                portals to other dimensions -- where the Great 
                Old Ones wait to take over the Earth. 

                                      PETER 
                Yeah?  Gimme an example. 

                                      EGON 
                Cthulhu. 

                                      PETER 
                Gesundheit. 

                                      WINSTON 
                Cthulhu -- I've heard of him.  He's bad, 
                right? 

                                      EGON 
                He makes Gozer look like Little Mary 
                Sunshine. 
A notorious episode of The REAL Ghostbusters, The Collect Call Of Cathulu (as it was misspelled in the opening credits) was the first of two episodes of this animated series (the second being "Russian About") to establish the Ghostbusters' location in the same universe of H.P. Lovecraft's Cthulhu mythos.

The episode was written by Emmy-award-winning (though not for this particular piece of work 8) Michael Reaves (as hired by then-series story editor J. Michael Straczynski, the author of Russian About and a proven Lovecraft fan in his other screen work) and primarily concerns itself with the Ghostbusters' attempts to recover a stolen copy of the Necronomicon as the alignment of the stars hints at something sinister in the eaves.

It features quasi-cameo appearances of characters based on or in homage to mythos writers Clark Ashton Smith, August Derleth, Robert E. Howard, Karl Edward Wagner and T.E.D. Klein and peaks with the entanglement of Cthulhu in roller coaster tracks, which are then charged to attract lightning, resulting in some Great Old One friccassee.

Reaves is on the record as having said he regretted the chance not to finish a script for a follow-up to this episode, A Fun Guy From Yuggoth. The script for this episode is viewable at http://www.mindspring.com/~michaelreaves/Cthulhu.pdf

Apparently there is also a West End Games module-supplement of this name for their The REAL Ghostbusters RPG based on this episode of the TV show. A gloss runs as follows:

    The Ghostbusters are called to investigate a burglary at the New York Public Library. The Library was staging an exhibition of some of the world's rarest books, including the Buggre All Thyse Bible and the mythical first edition of Alice's Adventures in Cleveland. However last night, someone broke in, attacked the security guard and stole one of the books. This book was the exceedingly rare 1577 John Dee edition of the Necronomicon...