A rapid build-up of pendent accelerator groups in the initial stages of vulcanization of natural rubber has shown that they are the precursors to the formation of crosslinks. Larger amounts of attached accelerator fragments were found for efficient and so-called sulfurless systems than for conventional accelerator-sulfur systems especially at short cure times. Cleavage of disulfides and polysulfides in the pendent groups by hexanethiol in piperidine showed a build-up of di- and polysulfides in the initial stages corresponding to that of accelerator fragments. Analyses were made by liquid scintillation counting using 14C-labeled accelerators. Due to the necessity of using liquid samples, vulcanizates were degraded in xylene solution with tert butyl hydroperoxide using osmium tetroxide as a catalyst. The use of a dual vulcanization system of dicumyl peroxide followed by the addition of sulfur and labeled accelerator by swelling techniques made possible the determination of accelerator fragments at short cure times when their concentration was the greatest. Polysulfides were found to have a profound and detrimental effect on the hardening of SBR during accelerated aging in air. An increase in attached accelerator fragments was found to take place during aging which may contribute to additional crosslinking and hardening.