The objective of this investigation was to determine the sulfuric acid (SO3/H2SO4) and sulfur dioxide (SO2) emissions from kraft recovery furnaces using an extractive sampling system. The Goksoyr and Ross controlled condensation technique was chosen. Equipment was designed and fabricated to evaluate the effect of coil length, grit porosity, temperature, flow rate, and concentration upon the efficiency of capture of H2SO4 in the modified Grahm condenser. The optimum design and operating conditions to minimize SO3/H2SO4 losses in filter holders used in the sampling train for particulate separation were determined, and the effects of recovery furnace particulate upon SO3/H2SO4 losses were investigated. Sampling of five representative Kraft recovery furnace stack gases showed that the SO3/H2SO4 concentrations varied from 0 to 2.98 ppm, while the range of SO2 concentrations was from 14 to 416 ppm. A comparison of these emissions with the SO3/H2SO4 and SO2 emissions from oil and coal fired utility boilers shows the kraft recovery furnace emissions to be much lower.