Abstract Oxygen appears to be essential for the absorption of phosphine by insects; under anoxic conditions phosphine is not toxic because it is not absorbed to any appreciable extent. Insects treated with cyanide to the point where respiration is inhibited or severely depressed, do not absorb much phosphine. Roaches treated in nitrogen or carbon dioxide are not visibly damaged by high concentrations of phosphine. Opening or closing of the spiracles appears to have little or no influence on absorption or on the toxic effect. After termination of exposure to an air-phosphine atmosphere, the muscular system of the roach continues to exhibit spasms which occur at increasing intervals until muscular energy is exhausted. The extent of injury produced in roaches appears directly related to the concentration of phosphine and is irreversible after termination of exposure. The amount of phosphine absorbed varies in different insect species; some become saturated within a 5-hr exposure period and absorb no more while others continue to absorb it at a slow rate for 24 hr or longer. After phosphine is taken up by the insects it is not desorbed.