The electrical conductivity of AgI has been determined to 100 kbar at room temperature, using a 1-kc/sec 20-V pulse as source. Conductivity increases with pressure in the low-pressure phase, stable to 2.5 kbar, and then decreases in the two high-pressure phases. The increase in the low-pressure phase is in agreement with its negative thermal expansion. A reversal of slope above 45 kbar in the cubic (NaCl-type) phase is explained in terms of the formation of I3−, recently reported from spectroscopic studies, in amounts decreasing with pressure to 70 ± 5 kbar, where I3− is no longer present.