Toroidal rotation of the central plasma core has been observed prior to and during electron cyclotron heating (ECH) in the Doublet III tokamak [inPlasmaPhysicsandControlledNuclearFusionResearch1984, Proceedings of the Tenth International Conference, London (IAEA, Vienna, 1985), Vol. 1, p. 131]. Measurements were made using a curved‐crystal Bragg x‐ray spectrometer with spectral resolution of &lgr;/&Dgr;&lgr; of greater than 19 000 and temporal resolution of 20 msec. Ion rotation velocity was determined from the Doppler shift of x rays emitted from the plasma impurity Ti XXI resonance line. Ion temperatures were determined from the Doppler broadening of this line. A study of purely Ohmic discharges suggests that nonrotating discharges exhibit magnetohydrodynamic activity other than sawtooth oscillations, while those that rotate exhibit sawteeth. Discharges with plasma rotation prior to the appliction of ECH appear to heat more effectively than those that do not. Velocity and temperature histories show that there are temporal characteristics corresponding to whether the plasma was or was not effectively heated.