BACKGROUND The Canadian Apheresis Group has maintained a national registry of apheresis activities for the past 16 years. Since 1991, the use of plasma as a replacement fluid in plasma exchange has been recorded. METHODS Six years of data from the registry on the use of plasma as a replacement fluid were analyzed. RESULTS Plasma was used in more than 25 percent of all plasma exchange procedures. Of 41,519 plasma exchange procedures reported, 11,970 used plasma alone or in combination with albumin. In 1991, 1026 (78%) of these procedures used plasma appropriately for either thrombotic thrombocytopenic purpura (TTP) or adult hemolytic uremic syndrome (HUS); between 1992 and 1996, these numbers were 1043 (81%), 1570 (86%), 1171 (87%), 2192 (92%), and 2741 (90%), respectively. In the remaining procedures, frozen or cryosupernatant plasma was administered to 326 patients for a total of 40 diseases other than TTP or HUS. CONCLUSIONS In those diseases for which plasma was administered as the sole replacement fluid, no disease appears to justify such treatment without the existence of an associated condition requiring specific replenishment of some plasma component. Further evaluation of the specific indications for the use of plasma as a replacement fluid in plasma exchange is required for diseases other than TTP or HUS.