The Lagrangian dispersion theory of Durbin is used to analyze experiments by Warhaft and Lumley [J. Fluid Mech. 88, 659 (1978)] and by Sreenivasanetal. [J. Fluid Mech. 100, 279 (1980)] on temperature fluctuations in grid‐generated turbulence. Both theory and experiment show that the decay exponentmdepends on the ratio of the initial length scales of velocity and temperature; although when this ratio is greater than 2.5 such dependence is negligible. The theory shows thatmis not truly constant, but within the range covered by the experiments it is nearly so. The agreement between theory and experiment lends credence to the idea that the decay of fluctuations is controlled largely by turbulent relative dispersion.