The application of monochromatic radiation pyrometry to measurement of plasma temperatures was investigated. Infrared emission and absorption spectra of nitrogen, argon, and helium plasmajets, with various admixtures, were measured. Strong infrared emission was observed in various lines and bands in the plasma spectra, extending from the visible region to 7.0 μ. The observed infrared absorption was generally low. Temperatures measured ranged from below 2000 deg K for a N2 plasmajet heavily seeded with CO2, to 13,000 deg K for pure Ar. Temperature gradients in a plasmajet were inferred from observations made through various regions of the jet.