The one‐dimensional equilibrium spectra in isotropic turbulence are given for the physical transfer theories of Heisenberg, Kova´sznay, and Obukhoff. These results are then compared with the experimental measurements of the spectrum of ∂3u1/∂x13fluctuations. For two of the theories (Heisenberg's and Kova´sznay's), reasonable agreement is obtained fork&eegr;< 0.04, but for larger values ofk&eegr;there is considerable divergence between the theoretical and experimental results. The relationship between the equilibrium and similarity spectra are also discussed for these two theories.