General properties of conductance histograms of atomic-scale metallic contacts are discussed. Nonlinear effects are included assuming a quasiadiabatic representation for electron transport. Histograms of conductance and histograms of differential conductance markedly differ when increasing the bias voltage. Averaging over different nanowire breakage paths at high bias rapidly smears out the peaks in IIV histograms, while it leads to new peaks at half integer values in dI/dV histograms. Recent experimental results on the histograms evolution with the applied bias are discussed.