Temperature coefficients in large reactors can be obtained from the transient response of the flux to oscillations of control rods. A method is described with which the coefficients can be measured under full operating conditions and without special instrumentation or access to the pile. Thus, the technique is particularly useful in measuring the dependence of the coefficients upon hydraulic conditions, power level, and fuel exposure. The waveform of the perturbing oscillation of reactivity is trapezoidal so that the regular reactor control system can be used. In large reactors the flux shape changes during the portion of the cycle when the control rods are moving, but only the magnitude of the flux changes significantly while the control rods are stationary. The flux response during this latter portion of the cycle is analyzed for the temperature coefficients. The pile kinetics equations, coupled with equations for the temperatures of fuel, coolant, and moderator, are solved for the flux during the imposed oscillation. The temperature coefficients and their delay times are found by fitting computed fluxes to the observed flux.