Dear Editor, Dr. Fluri and Mr. Templin make several misstatements in their defense of Pseudomonas pseudoalcaligenes. I feel a need to weigh in. First, Dr. Fluri is ill-informed regarding the current state of understanding about endotoxin.  The NOEL (No Observable Effect Level) for endotoxin vs. 1 sec. forced expiratory volume (FEV1) is 9 EU/m3. Concentrations of > 1,000 EU/m3 cause severe respiratory distress, and at >10,000 EU/m3 toxic shock is  likely.  Dr. Jillian Swan (British Institute of Health) surveyed aerosolized endotoxin concentrations at a number of UK metalworking plant and reported concentrations ranging from < 10EU/m3 to > 10,000 EU/m3.  Item 2: although great "blushes" of aerosolized endotoxin are likely to accompany shock treatment of a heavily contaminated system, it must be noted that both living and dead gram negative bacteria shed endotoxin.  The best way to prevent high airborne endotoxin concentrations is to minimize the endotoxin concentration in the recirculating fluid.  That means controlling the numbers of gram negative bacteria in the fluid. I'm glad that Dr. Fluri (& Mr. Templin) noted that DaimlerChrysler has only theorized that triazine overuse promotes the growth of Mycobacteria. Like P. pseudoalcalineges, Mycobacterium immunogenum, the putative etiologic agent for HP at MWF facilities, is ubiquitous.  It may be that the general practice of suppressing biodeteriogenic bacteria gives the slower growing mycobacteria an opportunity to flouish.  Triazine is the most commonly used active, so it takes the heat.  Unfortunately, DaimlerChrysler's action (banning triazine from in-formulation use) has been mis-interpreted as a triazine ban.  The intent is to compel coolant suppliers and fluid managers to use data (such as the oxygen demand test that Dom Ruggeri (you're welcome Dom - I'm glad you take good notes at my course presentations; although nowadays I find that a 2-h period is sufficient between the two oxygen readings) summarizes in his article to drive tank side biocide additions.  It's meant to reduce the use of in-concentrate biocide delivery since this approach is impossible to tailor to the conditions present in different MWF systems.  DaimlerChrysler still permits triazine use tankside. Finally, I'd be delighted to see the field data (perhaps a published paper) documenting airborne endotoxin concentrations proximal to a recirculating coolant system containing Blazcut plus 1E8 P. pseudoalkaligenes/mL being lower than the endotoxin concentrations around a system with < 1E4 total aerobic bacteria/mL.  If the work was done well, I'd be interested in seeing it published in METALWORKING FLUID MAGAZINE, where it can be subject to peer review. Fred Passman President, BCA, Inc.