1. A coaxial probe has been developed which allows measuring electrical resistivity of uncured carbon black-rubber compounds with good precision (mean coefficient of variation 4%). 2. For a given compound the resistivity correlates well with the standard dispersion rating and thus can be used for rapid monitoring of dispersion at various stages of processing. 3. Resistivity may also serve as a check on the loading and type of black in a rubber compound. 4. The resistivity of uncured compounds is higher by a factor of 2–10 than the corresponding vulcanizate value. 5. The logarithm of the resistivity appears to be a linear function of the reciprocal of the absolute temperature. The apparent activation energy of conductance for SBR compounds is 14.7–29.3 kJ/mol, the higher values being found for the better dispersions. The activation energies of EPDM compounds were found to be approximately 50% higher than those of SBR.