Organophosphate poisoning continues to be a major health problem in developing countries. The aim of this study was to investigate the effect of adding silymarin and carbamazepine to the standard treatment of organophosphate poisoning (atropine and oximes) on serial erythrocyte acetylcholinesterase and plasma butyrylcholinesterase activities after exposure to organophosphates, through an experimental and clinical research. The level of erythrocyte acetylcholinesterase activity was significantly high (p< 0.05) in carbamazepine treated rats 48 hours post-intoxication compared to the control group. A statistically significant (p< 0.05) in plasma butyrylcholinesterase activity was observed in silymarin treated group seven days following organophosphate exposure. The results of the clinical study showed a statistically significant (p<0.05) increase of both acetylcholinesterase and butyrylcholinesterase activities in silymarin add-on therapy compared to the control group, 72 hours following commence of silymarin therapy. A statistically significant increase (p < 0.05) in erythrocyte acetylcholinesterase activity in carbamazepine treated group compared to control group was seen at 48 and 72 hours after beginning of carbamazepine therapy. At last, the study brought to light a novel technique in assessing plasma butyrylcholinesterase activity through probing biological assay methodology employing isolated rat urinary bladder preparation.