The therapeutic effect of topical administration of zinc was tested in pregnant rats consuming a diet deficient in the element. Four groups of rats were fed a zinc-deficient diet for 24 hr. Half of the animals were treated during this period with a topical application of oil saturated with zinc chloride, for the full 24 hr in one group, and for the last 8 hr in the other. In the two remaining groups, oil without zinc chloride was applied under the same conditions as described above, and in all cases oral ingestion of the supplement was prevented. At the end of the 24-hr period, the animals were killed and plasma zinc was determined. An additional group of animals consuming a diet adequate in zinc was killed without any treatment to provide control values of normal plasma zinc. Rats consuming the deficient diet and without topical zinc supplementation had plasma zinc values significantly lower than all other groups after 24 hr. Animals receiving zinc supplementation for 8 hr had plasma levels similar to those of the control group fed an adequate zinc diet and significantly higher than those of rats that received no zinc application to the skin. In animals in which zinc was applied for 24 hr, plasma zinc values were significantly higher than in any other group, including normal controls. The results indicate that percutaneous transport of zinc may be of sufficient magnitude to be clinically significant and that topical application of this element may be useful in cases of dietary zinc deficiency or diseases producing a zinc deficiency state.