  I briefly review the formalism for treating the leading-twist two-gluon
states appearing in processes which involve eta and eta' mesons. The
constraints on the size of the lowest order Gegenbauer coefficients of the
two-gluon distribution amplitude are obtained from the fit to the eta and eta'
transition form factor data. The results are applied to chi -> eta eta (eta'
eta') decays and deeply virtual electroproduction of eta and eta' mesons.
