  Correlators of singlet and octet axial currents, as well as anomaly and
pseudoscalar densities have been studied using QCD sum rules. Several of these
sum rules are used to determine the couplings f^8_eta, f^0_eta, f^8_etaprime
and f^0_etaprime. We find mutually consistent values which are also in
agreement with phenomenological values obtained from data on various decay and
production rates. While most of the sum rules studied by us are independent of
the contributions of direct instantons and screening correction, the
singlet-singlet current correlator and the anomaly-anomaly correlator improve
by their inclusion.
