How to probe the spin-dependent gluon distributions

Two-spin asymmetries $A_{LL}^{\pi^0}$ are calculated for various types of spin-dependent gluon distributions. It is concluded that the E581/704 data on $A_{LL}^{\pi^0}$ do not necessarily rule out the large gluon polarization but restrict severely the $x$ dependence of its distribution. Moreover, $A_{LL}^{J/\psi}$ are calculated for the forthcoming test of spin-dependent gluon distributions.