1. Cats fed for 4 months with a diet with less than 7 p.p.m. zinc developed tissue zinc depletion, as judged by reduced muscle zinc content.
2. Dark adapted electroretinogram (ERG) thresholds became elevated in zinc depleted cats. Electroretinograms and muscle zinc levels were reversed by zinc supplementation.
3. Rod ERG to suprathreshold stimuli became reduced in b-wave amplitude in cats with zinc depletion, but suprathreshold cone ERG were unchanged.
4. The ERG changes in zinc depleted cats were unlike those in cats fed on a taurine depleted diet.