I. Standard zinc solutions for the atomic absorption analysis of rat plasma were prepared to contain 14 yo (w/v) of sucrose. In this way the problems of sample nebulization were overcome with a minimum of manipulation before assay.2. Plasma Zn concentrations in rats were found to fall by approximately 40 yo (from 1.2 to 0.7 pg/ml) after I d on a Zn-deficient (< 0.25 ppm) diet. Thereafter, the fall became less marked and after 5 d the concentrations usually varied between 0.4 and 0.6 pg/ml.3. A single oral dose (20-zoo pg) of Zn was reflected in high plasma Zn concentrations in the depleted rats 1.75 h after dosing, but to a much lesser extent in animals receiving 10-60 ppm Zn in their diet before dosing. 4. I t is suggested that the plasma Zn response to a single oral dose of zinc sulphate may provide a useful method for the detection of a subnormal Zn status in individual farm animals without the necessity of determining breed norms.

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