  We investigate the effects of low-lying fermion modes on the QCD partition
function in the epsilon-regime. With the overlap Dirac operator we calculate
several tens of low-lying fermion eigenvalues on the quenched lattice. By
partially incorporating the fermion determinant through the truncated
determinant approximation, we calculate the partition function and other
related quantities for Nf = 1 and compare them with the theoretical predictions
obtained by Leutwyler and Smilga.
