The resonance of saturated absorption in counterpropagating light fields is experimentally and theoretically studied. We
focus on a case of parallel and linearly polarized waves, driving an open dipole transition in rubidium vapor. A new
Doppler-free resonance within the saturated-absorption dip is revealed. The phenomenon can be gained only in
absorption of strong wave in presence of weak one. The effect can not be explained basing on the previously known
reasons. The results obtained can be found useful in metrology for the frequency and time standards.