The absolute detection efficiencies of a microchannel plate detector for neutral atoms were measured using the coincidence method for neutralized incident ions and ionized target atoms in electron capture collisions. This method does not require knowledge of the absolute electron-capture rates for determination of the detection efficiencies. Results for Ne, Ar, and Kr atoms at energies of 0.5-5 keV are reported. The detection efficiencies for all atomic species increase concomitantly with increasing impact energy and plateau at the efficiency of about 50%. For low impact energies, the efficiency decreases with increasing mass of the impact atom at a given energy.