Measurements of ion temperatures in the ATC tokamak by means of Doppler broadening of various ion lines are described, and typical results presented for the various auxiliary heating experiments: compression, neutral beam, lower hybrid and ion cyclotron frequency heating. Radial resolution of the temperature measurements is achieved by utilizing spectrum lines of ions of different ionization potentials: O VII λ 1623 Å, C V λ 2271 Å and C IV λ 1548 Å, which are emitted from regions of different electron temperature. Measurement at a given radial location is performed as a function of time by repeated scanning of the line contour in times 1.5–3.0 ms. The results indicate variations of heating efficiency with location and with power input level.