A study was made of the levels of reduced, oxidized and total G-SH in the blood of breeding bulls and in that of cows and their newborn calves immediately following parturition. Although diet within the limits employed in this study did not influence the concn. of glutathione of either form in bulls'' blood, the levels of reduced and total G-SH gradually increased as age progressed from 18-33 mos. Following parturition, similar levels of G-SH were found in the blood of cows ranging from 29-155 mo. of age. Ca fed 2 mo. prepartum as the only supplement and in conjunction with various trace elements in a basic dry-cow feed did not significantly affect the levels of G-SH of either state in the blood of the dams or their newborn calves as detd. in blood taken soon after parturition. The blood of the calves, however, contained significantly greater quantities of reduced and total glutathione than that of their dams or of any of the animals studied. Calves having ingested colostrum before blood was obtained for analysis, at an avg. age of 4.5 hrs., showed markedly lower concns. of reduced and total G-SH than those which had not received this food. These data suggest a rapid decline in blood G-SH during the early life of the calf. Similar levels of G-SH were found in the blood of newborn calves regardless of sex. Age, sex, and diet did not appear to be related to the level of oxidized G-SH, as the concn. of this compound was similar for all animals studied. The failure to measure ozidized G-SH in the blood of bulls yielding large quantities of semen was attributed to changes occurring in the blood under these conditions which inhibit the reduction of oxidized G-SH by metallic Zn.