The objective was to evaluate the ability of the Test-mate ChE to determine acetylcholinesterase (AChE) activity under field conditions. To mimic nerve agent exposure, the U.S. Army Medical Research Institute of Chemical Defense spiked blood samples with variable amounts of soman. Blinded to the identity of the samples, the 520th Theater Army Medical Laboratory tested the samples during a field training exercise inside their environmentally controlled mobile facility. The technicians repeated measurements for 6 consecutive days, and on 1 of the days repeated the measurements six times. The technicians accurately identified all of the samples and quantified the AChE activity. The major trend was that the Test-mate ChE is more precise and reproducible for smaller doses of soman. The results were reliable over all temperatures during the field exercise. In conclusion, the Test-mate ChE is a reliable field instrument to determine blood AChE activity.