High level disinfection (HLD) of GI endoscopes can be reliably obtained with approved reprocessing methods. However, there are scant data regarding the effectiveness of these methods in clinical practice and no published methods to verify HLD. Since 1991 we have periodically cultured flexible endoscopes to monitor the quality of daily reprocessing procedure (RP). The purpose of this study is to retrospectively review the results of these environmental cultures (EC) and analyze the pattern of results. Methods: EC of randomly selected “ready to use” GI endoscopes and water bottles (WB) were obtained by adding 15ml TSB broth, saline, or 30-50ml sterile water to the biopsy channel of an endoscope. These were collected, plated, incubated, & examined @ 24/48hrs. Our EC cost is $5.00/culture. Trained personnel performed all scope reprocessing with glutaraldehyde/automated washers. Results: In 1991 3/17 WB were contaminated with Pseudomonas. Sterile water & WB were then used daily & all subsequent WB were culture negative (EC-). Between 1992-4 15/129(12%) were postive (EC+), 3(2%) were gross positive(GrEC+) with = 103 col & 14/15(93%) were from duodenoscopes(DS). RP for DS was altered & from 1995-7 18/124(15%) were EC+, 3/124(2%) were GrEC+, but only 6/18(33%) were from DS. 10/18(56%) were from therapeutic scopes (TS), attributed to faulty mechanical cleaning by untrained personnel after emergent procedures. RP was altered with improvement in EC results. In 1998 0/10 were EC+. Overall, DS were EC+ 15%, TS 16%, but standard scopes 7%(0% GrEC+). All scopes were EC- after repeat RP but one DS which, repeatedly EC+ with identical organisms, was found at repair to have a damaged biopsy channel & remained EC- after repair. There were no recognized iatrogenic infections. Organisms were commonly gram neg rods. Conclusions: 1)The use of EC is a simple, rapid & inexpensive monitor of effectiveness of standard RP. 2)HLD is less effective with poor mechanical cleaning & high titer positivity(GrEC+) is a marker for poor technique which requires retraining. 3)Standard scopes are commonly EC- & none were GrEC+. 4)DS (due to inherent complexity of scope & procedure) & scopes used in emergencies require particular attention. 5)EC results can be used to identify patterns of poor technique, reinforce proper procedure & modify clinical practice.