Selenium is an element necessary for good animal health. No information is available on inheritance of Se concentration in tall fescue (Festuca arundinacea Shreb.). Therefore, the purpose of this investigation was to determine the nature of genetic variation of Se concentration in tall fescue. To accomplish this objective, 15 parental clones were randomly chosen from a broad-based population, and their half-sib (HS) progenies were generated using a polycross mating design. Selenium analysis was determined flourometrically by digesting dried, ground herbage samples in 3:1 HNO3/HCIO4. Significant genetic variation was observed among HS families in the fall for Se concentration. Heritability, calculated using parent-offspring (PO) regression, gave estimates of 18% for summer and 68% for the fall. Heritability and genetic gain estimates were maximized in the fall, as compared with the summer, largely because of a large environmental component. Genetic gain, expressed as a percentage of the mean of parents, predicted an advance of 1 9 % for fall herbage. Progress in selecting for improved concentrations of Se in the fall in this population of tall fescue is likely.INHERITANCE of mineral concentrations in cool-sea-1 son forage grasses has largely concentrated on the elements Mg, Ca, and K (Sleper et al., 1989). These three elements have received attention by forage grass breeders because of their importance in grass tetany or hypomagnesemia. Grass tetany of ruminants is associated with low blood-serum Mg levels (Kemp,