The interactions of silica in zinc-activated, sulfur-vulcanized cis-1,4 polyisoprene were characterized at the 75% cure state using H-1 NMR imaging spectroscopy. Variables examined included silica loading, mixing conditions, and presence of additives, including a coupling agent and polyethylene glycol. Rheometer curves indicated a decrease in cure rate and cure state as silica was increased. H-1 NMR imaging showed an increase in the T-2 relaxation times, and a decrease in the proton spin density N(H) as the filler load increases. Mixing conditions did not affect the cure rate, cure state, or the average T-2 relaxation time; however, the distribution of relaxation times broadened with poor mixing. The presence of a coupling agent increased the cure rate and cure state, as well as decreased the T-2 relaxation times as compared with samples with the same silica level, but without coupling agent. Polyethylene glycol (PEG) had slightly higher average T-2 relaxation times, and a slightly broader distribution as compared with the sample without PEG added.