(NIOSH/CDC, 1996-2001) This study evaluated the accuracy of cholinesterase determinations performed on the EQM Testmate Kit??? in field conditions as compared to those conducted in a laboratory. It also examined whether a field-based kit provides advantages in promptness of worker removal. Seventy-five orchard workers with regular exposure to Guthion, Diazinon, and several other organophosphate and N-methyl carbamate pesticides had samples of their blood and urine taken during the growing season. Samples were also obtained from five unexposed workers. Both the Testmate Kit and conventional venous laboratory testing for plasma and erythrocyte cholinesterase measurements were performed on the samples. Urinary metabolites confirmed that exposure was occurring in the exposed group but no significant mean cholinesterase changes were noted with either laboratory or field based methods. Preliminary findings indicated relatively good performance of the Testmate Kit under field conditions as compared to the laboratory.