This paper presents experimental results of aerosol penetration through a wire screen for mobility-equivalent particle diameters between 2 and 10 nm, Reynolds numbers for the fluid approaching the screen (Re-t) between 300 and 6000, Peclet numbers (Pe) between 20 and 13 000, and wire diameters between 40 and 100 mum. An empirical expression, eta (D) = (2.53 + 5.14 x 10(-4) Re-t)Pe((-0.65 + 2.5 8 x 10 -5Ret)), correlating the single fiber efficiency, eta (D), With the Peclet and Reynolds numbers has been obtained. In the limit of very low Reynolds number (Stokes regime) the above expression reduces to eta (D0) = 2.53Pe(-0.65) which is in good agreement with the widely accepted correlation for fan model filters, eta (D0) = 2.7Pe(-2/3), of Cheng and Yeh.