Gas phase diagnostics with multispecies diatomic spectra isdiscussed. Analyses of spectra from the A(3)?(i) ? X(3)?(-) system of NH and the C(3)?(u) ? B(3)?(g) second-positive system of N(2) are presented. Multispecies spectroscopy is applied to experimental spectra obtained from laser-induced breakdown plasmas in anhydrous ammonia gas and a low-pressure discharge lamp.