Dog tissues were incubated in vitro with cortisol-4-14C in the presence of ATP. The radioactive sulfoconjugated product was isolated and identified as cortisol-21-sulfate. It was found that not only the adrenal and liver, the known sites of corticosteroid sulfation, but other tissues such as kidney, diaphragm and lung were also capable to sulfurylate cortisol. Their percentage conversions were as follows: the adrenal 1.7 liver 1.7, kidney 5.7, diaphragm 0.7, lung 0.6. Spleen, intestine and brain were devoid of the capacity. The possible presence of cortisol sulfate in dog's circulation and the contribution of these tissues as the sources of the conjugate were discussed. (Endocrinology90: 1404, 1972)