A monitoring method was developed to determine mean concentrations of pesticides in air for a long period in a week. The pesticides investigated were fenitrothion, malathion, fenthion, phenthoate, tetrachlorovinphos, edifenphos, pyridaphenthion and fenobucarb. Air was sampled into a glass column with 115 mm by 17 mm i.d. (3 mm i.d. at both sides) packed with 5 g of activated carbon (Calgon BPL of 35 to 60 mesh) at 0.1 to 0.5 l/min for 7 d. The sampled pesticides were eluted from the activated carbon column by 100 ml of benzene at 0.5 ml/min. The eluate was concentrated to 0.3 ml for the determination by use of gas chromatography on a glass column with 2 m by 3 mm i.d. packed with 5% silicone DC-200 on Chromosorb W AW-DMCS (60 to 80 mesh). A flame thermionic detector was used for fenobucarb and a flame photometric detector for the others. The desorption efficiencies of the pesticides from activated carbon column were ranged from 77 to 99%. Recoveries of the pesticides on the overall performance of this method were 73 to 95% ; the minimum determinable concentrations were 0.05 ng/m³ (for fenitrothion) to 0.23 ng/m³ (for edifenphos). This method was applied to determine the pesticides in rural areas in Niigata Prefecture from May, 1988 to March, 1989 ; fenitrothion, edifenphos, pyridaphenthion and fenobucarb were detected from May to October.