BACKGROUND: The Washington State Cholinesterase Monitoring Program for pesticide handlers requires blood draws at local clinics, with samples tested at a central laboratory. At present, workers with inhibited cholinesterase activity may be re-exposed before they can be removed from work. In this study we explored the option of on-site testing at local clinics using the EQM Test-mate Kittrade mark, a portable cholinesterase test kit. METHODS: Test kit cholinesterase activity measurements were performed on 50 blood samples by our research staff, and compared to measurements on the same samples by the Washington State Public Health Laboratory. Another set of samples was also analyzed with the test kit by medical staff at an eastern Washington clinic. RESULTS: Triplicate measurements with the test kit had a 3.3% average coefficient of variation (CV) for plasma cholinesterase (PChE), and a 3.5% average CV for erythrocyte cholinesterase (AChE) measurements. The kit's PChE measurements were similar to PHL measurements (average ratio of 0.98) when performed in the laboratory, but had a tendency to underestimate activity when used in the clinic setting (average ratio of 0.87). The kit systematically overestimated AChE activity by 42-48% relative to the PHL measurements, regardless of where the samples were analyzed. CONCLUSIONS: This easy-to-use test kit appeared to be a viable method for clinic-based PChE measurements, but was less consistent for AChE measurements performed in the clinic. Absolute measurements with the kit need to be evaluated carefully relative to standardized methods. (c) 2008 Wiley-Liss, Inc.