The efficiencies of impaction of Lycoperdon spores and Paper Mulberry Pollen on cylinders, ribbons, discs and spheres have been determined by a direct counting method. The results are compared with theoretical calculations based on potential and viscous flow régimes and indicate that finite collection efficiencies occur at values of the inertial parameter, K, less than the critical value, Kc, relevant to the collector. Generally the experimental points lie between the potential and viscous flow curves, those points for Reynolds number, Re, of the flow less than about 50 being notably depressed towards the viscous curve, while those for Re > 200 lie close to the curve for potential flow. Angles-of-trace, θm, for spheres and cylinders, allowing for the effect of finite Reynolds number, agree quite well with the calculated values of Langmuir for potential flow but it is observed that θm is always finite even when K < Kc.