High selenium barley biscuits containing 1 mmol (70 micrograms) organic Se were administered to healthy male volunteers for 5 weeks at doses of 2.1 mmol Se (group A) or 6.4 mmol (group B). In addition, 2 mg Na-selenate capsules (5.4 mmol Se) were given to two other groups at daily doses of 2 mg (group C) or 8 mg (group D). Groups A, B and C each comprised eight healthy men and group D eight healthy women and three men. The initial median concentration of whole blood selenium (B-Se for groups A, B and C were 1.0-1.1 mumol/l (range 0.7-1.7) and for group D 1.3 mumol/l (range 0.9-1.8). In 1-2 weeks time the B-Se concentrations rose to 1.6 mumol/l for groups A and C, to 1.8 mumol/l for group B, and to 2.2 mumol/l for group D. There was no decrease 1 week after the Se intake ceased. As expected, the level of B-Se increased more (in relation to dose) in those given organic Se than in those given inorganic Se. Groups A, B and C, however, had rather moderate increases. The daily dose required to raise the B-Se of Finns up to the North American level (2.2 mumol/l) was as high as 8 mg Na-selenate (21.5 mumol or 1700 micrograms Se), but the dose of organic Se which would be required to achieve this level is not yet known.