A vitamin and trace element supplement containing recommended dietary amounts or "safe and adequate" levels was given to ten healthy subjects for 12 to 35 weeks. Plasma levels of selenium and zinc, activity of glutathione peroxidase in plasma and platelets, whole blood manganese, activity of superoxide dismutase in hemolysate, activity of alkaline phosphatase in serum, iron status indices and urinary excretion of zinc and selenium were measured. A small but significant change in plasma selenium from 1.01 +/- 0.14 mumol/L to 1.08 +/- 0.10 mumol/L was observed after two weeks. However, at the end of the supplementation plasma selenium levels did not differ from the initial levels. Plasma glutathione peroxidase levels showed a similar trend and changes in glutathione peroxidase activity in platelets were also transient. A small increase in serum zinc values was observed after 30 weeks of supplementation. No significant changes were observed in the other blood and urine parameters studied. In seven of the subjects absorption of zinc, manganese and selenium was measured after 30-31 weeks of supplementation by a radionuclide technique. The absorption of selenium and manganese after long term supplementation was 30-50% lower than observed previously in non-supplemented subjects. In conclusion, present available indices of trace element status are only to a limited extent affected by 30 weeks of a doubling of the normal dietary intake.