A technique for producing very small spheres of a viscous solution of DDT in lanoline is described. Spheres of a saturated solution, 1·77 × 10 −3 μl in volume, possessing a reserve of DDT crystals, were applied to structurally different parts of the integument of Phormia terraenovae R-D. The quantities of DDT absorbed in 48 hr were measured for several parts of the body and the rates of absorption of insecticide at two parts of the head were determined. The results indicate that after a short initial period the rate of diffusion of insecticide molecules through the cuticle was governed by the hypodermal cells.