"Erythrocyte and plasma selenium and glutathione peroxidase specific activities, hair and fecal selenium, and urinary selenium excretion were increased by and were linearly related to L-selenomethionine dose. Hair selenium was most sensitive to L-selenomethionine dose, with an 84-fold increase in the 300 micrograms selenium/(kg-d) group relative to controls (r = 0.917). Daily urinary selenium excretion (80-fold, r = 0.958), plasma selenium (22-fold, r = 0.885), erythrocyte selenium (24-fold, r = 0.920), and fecal selenium (18-fold, r = 0.911) also responded strongly to L-selenomethionine. Erythrocyte and plasma glutathione peroxidase specific activities increased 154% and 69% over controls, respectively. Toxicity was associated with erythrocyte selenium > 2.3 micrograms/mL, plasma selenium > 2.8 micrograms/mL, and hair selenium > 27 micrograms/g. Plasma, erythrocyte, and hair selenium concentrations may be useful for monitoring and preventing the toxicity of L-selenomethionine administered to humans in cancer chemoprevention trials.."

(Hawkes WC; Willhite CC; Craig KA; Omaye ST; Cox DN; Choy WN; Hendrickx AG. Effects of excess selenomethionine on selenium status indicators in pregnant long-tailed macaques (Macaca fascicularis). Biological Trace Element Research, 1992 Dec, 35(3):281-97.)