Three compounds, apholate (2,2,4,4,6,6-hexahydro-2,2,4,4,6,6-hexakis (1-aziridinyl)-1,3,.5,2,4,6-triazatriphosphorine), aphoxide (tris(1-aziridinyl)phosphine oxide), and methaphoxide (tris (2-methyl-1-aziridinyl)phosphine oxide), induced sterility in male and female stable flies ( Stomoxys calcitrans (L.)) when applied topically to adults. One microgram of apholate or methaphoxide per fly caused almost complete sterility when treated males were mated with treated females. Male stable flies were more sensitive to apholate and aphoxide than the females. Apholate sterilized adult stable flies even when applied after the females had begun laying fertile eggs. Apholate induced sterility when adults were exposed to a residual film. A 48-hour exposure was required with a film of 10 mg. per ½-pint jar. However, a film of 100 mg. per jar was effective with all exposure of I hour. When treated jars were stored indoors, the film was effective for 24 weeks.