The effect of halothane anesthesia in different doses and a period of two weeks on glucose-6-phosphate dehydrogenase (G6PDH) activity of mouse liver were investigated. The mean and SD of G6PDH for liver of normal mice were 0.036+/-0.017 U/mg protein and 1.756+/-0.814 U/g liver, respectively Although there was histopathological damage in the liver, liver weights in treated mice increased significantly compared to control animals. Increasing the dosage of halothane inhalation induced liver G6PDH enzyme activity (U/g liver) by 84%, 42% and 4%, showing an inverse relation with the dose of halothane (0.25, 0.50, 1.00 cc thrice daily for two weeks). Although the Michaelis constant (Km) of the partially purified enzyme for glucose-6-phosphate (G6P) and nicotinamide adenine dinucleotide phosphate (NADP) were similar, the utilization of analogs as 2-deoxyglucose-6-phosphate (2d-G6P), galactose-6-phosphate (Gal-6P) and nicotinamide adenine dinucleotide (NAD) were different. The induced enzyme was more heat stable than the control.