Hydrogen cyanide gas (HCN(g)) is released from CIP/CIL slurries through either entrainment in the air/oxygen injected into the tanks, or through direct evolution from the pulp surface. The HCN(g) released by entrainment has been measured by placing capped pipes over aerated/oxygenated tanks to collect the evolved gas. The collected gas was passed through a scrubber to remove the HCN(g). The scrubber solution was then titrated for cyanide, giving a measure of the HCN(g)) released by aeration/oxygenation. HCN(g) evolved directly from the pulp surface was measured using capped pipes that were modified to have nitrogen injected into the pipe close to the slurry surface. The injected nitrogen then carried the HCN(g) from the pulp surface to the scrubber. The nitrogen was injected at a rate sufficient to ensure that HCN(g) loss from the surface was under diffusion control. HCN(g) emission from the tanks of the CIP circuit surveyed accounted for approximately 1 % of the total cyanide added, with the majority of that being evolved directly from the pulp surface. The rate of HCN(g) evolution from the tanks was found to be directly proportional to the HCN(aq) concentration in the pulp liquor.