This study examined the relationship between zinc absorption and metallothionein. Mice injected intraperitoneally with ZnCl2 (2 mmoles) were found within 18 hours to have increased levels of intestinal metallothionein but an apparent decrease in 65Zn absorption. Induction of metallothionein with lower levels of ZnCl2 (0.2 or 0.5 mumoles) resulted in an apparent increase in 65Zn absorption. Isotope dilution experiments showed that intraperitoneal injections of 2 mumoles of ZnCl2 had resulted in a 500-fold dilution of the available 65Zn pool. Mild stress of the animals was shown to increase both 65Zn absorption and intestinal metallothionein. Actinomycin D administered 4 hours prior to ZnCl2 or stress, prevented the induction of metallothionein and obliterated the increase in 65Zn absorption. These results indicate that zinc absorption is directly proportional to intestinal metallothionein levels and imply a significant role for metallothionein in zinc absorption.