Since its introduction in 1994, the Parallel Sysplex architecture for mainframe computer systems has attracted a great deal of interest because of its high performance, continuous availability, scalability, and lower cost of ownership. Recently, it has become possible to interconnect the building blocks of a Parallel Sysplex (host processor, coupling facility, sysplex timer, and disk storage) at extended distances using fiber optic data links. In particular, optical wavelength-division multiplexing (WDM) has been an enabling technology for the extension of this architecture to a geographically dispersed Parallel Sysplex (GDPS). We describe the use of WDM in GDPS configurations, including distance limitations and typical performance considerations. Experimental results of testing a GDPS with WDM channel extensions up to 40 km are presented, and some test results on the IBM 9729 Optical Wavelength Division Multiplexer used in these configurations are also discussed.