Sign balance for finite groups of Lie type

A product formula for the parity generating function of the number of 1's in invertible matrices over Z_2 is given. The computation is based on algebraic tools such as the Bruhat decomposition. The same technique is used to obtain a parity generating function also for symplectic matrices over Z_2. We present also a generating function for the sum of entries of matrices over an arbitrary finite field F_q calculated in F_q. These formulas are new appearances of the Mahonian distribution.