Pre-adult stages of Sitophilus granarius in wheat were exposed to concentrations of 0.01-0.24 mg/l of phosphine for periods of 3- 14 days at 25 degrees C and 70 per cent rh. In one test, samples were preserved at intervals and later dissected. These showed that development continued during fumigation. It was also demonstrated that adults laid viable eggs during fumigation at these concentrations. The results suggest that all the pre-adult stages reached a susceptible stage of development during a 10-day fumigation so that this period produced complete mortality.