1. A method of studying zinc absorption in rats has been developed in which binding of radioactive Zn to the intestinal mucosa and absorption into the carcass was determined at different times after administration by stomach tube. 2. This technique has been used to evaluate different hypotheses concerning the control of Zn absorption and to examine the processes by which this occurs. 3. The proportion of radioactive Zn absorbed into the carcass was found to be dependent on the Zn status of the animals but that found within the small intestinal wall was independent of this, indicating the existence of two mechanisms of Zn absorption. 4. One of these two mechanisms has been shown to be induced by a low dietary Zn content while the other was shown to be insensitive to this. This latter mechanism predominated in rats of normal dietary Zn, status and a study of the characteristics of this process indicated that the quantity of Zn absorbed was proportional to the dietary Zn content over the normal range of intake. This implies that normally Zn homeostasis in rats is achieved through variations in Zn excretion. The additional mechanism of Zn absorption only becomes fully active at levels of dietary Zn below 0.24 MUMOL/g diet.