Thyroid hormone profiles were determined in two groups of dogs mode uremic, either by i.v. uranyl nitrate 10 mg/kg BW injection or by bilateral ureteral ligation, and in one group of sham-operated animals. Each group consisted of 6 dogs and served as its own control. From blood samples taken in 12-h intervals up to 144 h for uranyl nitrate-injected dogs and 96 h for operated dogs, serum levels of T4, T3, fT4, fT3, rT3, and cortisol were measured by radioimmunoassays. The results obtained in both groups of uremic dogs showed an initial sharp fall of T4, T3, fT4, and fT3followed by a plateau or retarded decrease. In sham-operated dogs the fall of these hormones was slight and of short duration. Reverse T3had a tendency to increase in all groups examined, but a significant elevation was recorded only after bilateral ureteral ligation. In this group cortisol serum levels were found the highest, being also significantly increased in the other two groups. The temporal coincidence of the most marked alterations in T3, rT3, and cortisol serum concentrations indicates a significant role of stress in thyroid dysfunction. Although serum creatinine rise and weight loss were not parallel with thyroid hormone alterations, the involvement of uremic compounds and malnutrition in this process is also quite clear. Thus, the data presented suggest simultaneous influences of uremic toxins, stress, and malnutrition on the induction of thyroid dysfunction in dogs made uremic by uranyl nitrate injection or bilateral ureteral ligation. Certain different features in defined thyroid hormone profile are probably related to the intensity of factors realized through the methods used and variate with the time elapsed from the onset of acute renal failure.