It has been reported, by other authors [1-3], that under DC plasma conditions the diffusion of C into Fe is much greater than that obtained under thermal equilibrium conditions. They postulated that the exceptionally high C uptake is due to rapid infusion (mass transfer) of C into the surface from the plasma, and not to an anomalously high diffusion rate in the bulk. The aim of the current investigation was to determine whether the rapid infusion of C and classical C diffusion rates obtained from high CH4 concentration plasmas are also observed in the lower C content (1% CH4) plasma employed in CVD diamond deposition. A series of experiments were conducted for short deposition times (up to 5 min) under plasma-CVD diamond deposition conditions at a substrate temperature of 950 degrees C. The C profile was analysed using Auger electron spectroscopy (AES) and Rutherford backscattering spectroscopy (RES). The diffusion coefficient (D-o) calculated from thermodynamic data for 950 +/- 20 degrees is (3.0 +/- 0.6) x 10(-11) m(2) s(-1), whereas that estimated from the AES depth profile using a constant surface concentration solution to Fick’s second law was found to be 4.2 +/- 1.3 x 10(-10) m(2) s(-1). Hence, even though the carbon content in the plasma is very low the diffusion occurring under plasma conditions at a sample temperature of 950 +/- 20 degrees C is equivalent to that expected from thermal diffusion at 1244 +/- 42 degrees C. Possible mechanisms for this enhancement are discussed.