The effect of high-abrasion furnace (HAF) carbon black on the course of the tetra-methylthiuram disulfide-accelerated sulfur vulcanization of natural rubber has been investigated at temperatures from 100°C to 140°C. Continuous measurements in a Vuremo curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. Results now available show (1) HAF carbon black does not alter the mechanism of the thiuram-accelerated sulfur cure; it also has no qualitative effect on the kinetics of the vulcanization reactions involved. (2) Quantitatively speaking, essential differences take place. The rate constants of vulcanization rise considerably when HAF carbon black is used; there is a dependence on the HAF carbon black content of the rubber compound. Yet the activation energies of vulcanizations are practically the same as in carbon black-free mixture, amounting to about 31 kcal/mole. (3) Measurements of the course of vulcanizations prove the reinforcing effect of HAF carbon black.