PHENOMENOLOGICAL EVIDENCE FOR THE GLUON CONTENT OF ETA AND ETA'

We discuss the effect of eta-eta' mixing and of axial current anomalie s on various decay processes. We describe the 2 gamma decays of eta an d eta' the radiative decays of low-lying vector mesons as well as the decays eta --> 3 pi, J/psi --> eta gamma and J/psi --> eta'gamma in on e unified framework, in which they are related to the electromagnetic and strong axial current anomalies, respectively. We also discuss brie fly the enhancement of eta' in D-s decays and suggest a possible relat ion to gluon-mediated processes. The importance of the decays of the g lueball candidates f(0)(1500) and f(0)(1590) into eta eta' channels is also stressed.