Studies were performed on the nature and magnitude of the variabilities in the rheological and processing properties of purified natural rubber (PNR). PNR samples were prepared from three clones of NR (RRIM 600, GT 1, and KRS 156). The corresponding whole NR (WNR) containing total nonrubber substances was also prepared for comparative purposes. All samples were stored for 3 months to elucidate the effect of storage on their rheological and processing properties. A novel study was also conducted to determine whether the commonly reported variabilities in the rheological properties had actual effects on the mixing. These were studied by means of an instrumented torque rheometer fitted with a small mixer head. The results showed that the vulcanization time of PNR was consistent and did not show clonal variation. PNR exhibited large clonal variation in the viscosity at a low shear rate and storage hardening, similar to the ordinary NR. However, the variations in the viscosity of PNR became less evident as the shear rates increased toward 200 s(-1). The significant findings were that the observed variations in the rheological properties had no practical effect on the mixing time of PNR samples with carbon black. Moreover, the PNR samples required less energy for mixing than their WNR counterparts. (c) 2005 Wiley Periodicals, Inc.