Acute organophosphate poisoning (OPP) such as dichlorvos may be monitored by the measurement of the erythrocyte acetyl cholinesterase (EAChE) and the serum cholinesterase (SChE) activities. The aim of this study was to look at correlation between the severity of the OPP judged by certain parameters such as coma, hemodynamic disturbances, respiratory failure, and the decrease of cholinesterases enzymes including EAChE and SChE at admission. Cholinesterase activity was determined upon admission and then on days 3 and 15 in the morning. Clinical effects, EAChE, and SChE activities data were investigated in 42 patients with OPP aged of 29.6 +/- 11.8 years with acute cholinergic crisis in all cases. They were comatose in 29% of cases, presenting both hypotension or shock and hypoxemia in 17% of cases. Fifteen of them (36%) required mechanical ventilation. The mean EAChE activity at admission was 24.3 +/- 11.6 micromol/mL per hour at 37 degrees C; it was 1260 +/- 2204 IU/L for SChE. There were no correlations between the EAChE and the SChE activities. The EAChE was decreased only in comatose patients and those presenting hypotension, hypoxemia, and bradycardia with a cutoff of 23.5 micromol/mL per hour at 37 degrees C. Death was observed in 2 patients with a deep decrease of the EAChE at 5 micromol/mL per hour at 37 degrees C in 1 case and 9 micromol/mL per hour at 37 degrees C in another. The kinetics of improvement of the EAChE activity below the cutoff showed the absence of statistical improvement of the EAChE activity on day 3 (16.6 +/- 9 vs 19.5 +/- 5.7 micromol/mL per hour at 37 degrees C); this improvement was remarkable on day 15 (16.6 +/- 9 vs 27.5 +/- 6.5micromol/mL per hour at 37 degrees C, P = .0004). In summary, the marked decrease of EAChE activity appears in this study as prognostic factor in acute OPP, and coma, respiratory failure, hemodynamic disturbances, and death are associated with a decrease of the EAChE of less than 23.5 micromol/mL per hour at 37 degrees C.