1. The effect of treating rats with digoxin and thyroxine for 45 days has been studied.
2. Animals fed with digoxin gained significantly more weight than the control animals.
3. Treatment with digoxin, thyroxine or both produced a similar significant increase in the amount of Na+ + K+-dependent adenosine triphosphatase in liver without an additive effect.
4. It is suggested that digoxin resistance in thyrotoxicosis may be related to this similarity in action.