The horizontal and vertical movements of chloropyrifos (Dursban 48%) and its biological activity on the workers of the two subterranean termites Anacanthotermes ochraceus (Fam. Hodotermitidae) and Psammotermes hybostoma (Fam. Rhinotermitidae) was investigated in a sand loamy soil at El-Fayoum Governorate, Egypt. Cylindrical holes (30cm in diameter, 30cm deep and 3m apart) were treated with chloropyrifos at the recommended dose (1% a.i. aqueous emulsion at a rate of 4 liters/ hole). Soil samples were taken from the treated holes at different horizontal and vertical distances from treatment locations at 1, 7, 30, 90, 180, 270 and 360 days after treatment and the mortalities of the workers of the two considered termite species determined after 3 days of exposure to treated soil. The residues of chloropyrifos at the different tested horizontal and vertical distances combinations at the different sampling dates were also determined. Chloropyrifos penetrated into the soil horizontally to distances of at least 60cm from treatment locations from all directions, vertically upwards to distances of at least 10cm above treatment locations and vertically downwards to at least 60cm below them from all directions. Chloropyrifos persisted in the treated soil for at least 360 days with a maximum residue of about 400ug/ g at treatment location 1 day after treatment and a minimum residue of about 236ug/ g at the same location 360 days after treatment. The efficacy of chloropyrifos decreased with its penetration into the soil either horizontally or vertically along with time. Chloropyrifos remained considerably effective against the workers of both A. ochraceus and P. hybostoma as long as its residue in soil recorded about 2ug/ g or more. The horizontal movement of chloropyrifos in soil indicated that the recommended horizontal distance between any two holes for an effective control of termite workers in a sand loamy soil is 60cm from all directions.