Organophosphate pesticides, commonly used in the occupational field, represent a real threat to human health and the environment. The aim of our study is to estimate the level of knowledge of the subjects exposed to these products and assess their toxicity biomarkers. We conducted a prospective descriptive survey about 26 pesticide handlers who checked in occupational medicine service in Hedi Chaker university hospital. A questionnaire allowed us to gather information about the level of workers education and their practices of organophosphate pesticides spacifically Fenitrothion. Three samples of blood and urine tests were collected before and after exposure and after rest in hygiene service. Each blood sample was used for the determination of serum and erythrocyte cholinesterase activity. The detection of organophosphate pesticides was made in the urine by GC/MS. A low level of knowledge of the manipulators for pesticides (global score was 20.46) was found. Reference globular cholinesterase activities were all below the usual values. Serum cholinesterase activities were decreased by 30 to 50% in 48% of patients and more than 50% in 30% of the subjects. These activities have recovered after rest. The detection of pesticides (fenitrothion) was positive in 4 workers. Biological assays show impregnation of manipulators by organophosphate. Their kinetic reflects the exposure of subjects with the pesticide. These data were correlated with the low level of workers knowledge (p=0.01).