The absorption of zinc and iron was determined in seven elderly men using the enriched stable isotopes 70Zn and 58Fe. Analyses of isotopic ratios were done using thermal ionization magnetic sector mass spectrometry on chloride solutions of zinc and of iron after separation of zinc from fecal samples by ion exchange and of iron by solvent extraction. Mean apparent zinc absorption in the seven subjects was 17.3 +/- 3.1% (mean +/- SEM) and mean iron absorption was 7.9 +/- 2.5% (mean +/- SEM) when fed a semipurified diet containing 15 mg of zinc and 10 mg of iron daily. Quantities absorbed were equivalent to an average of 2.6 mg of zinc and 0.8 mg of iron per day. These average zinc and iron values are close to previous estimates of endogenous losses of zinc and iron.