Although it had been known that copper rapidly oxidizes the beta-hemes of hemoglobin, it was found that copper will also oxidize the alpha-hemes, but at a rate of only about 20 1/M/sec at pH 6, about a thousandth as fast as for the beta hemes. If the rapid oxidation of the beta-hemes is prevented by reacting the B-93 sulfhydryl groups with mercury or an organic thiol reagent, copper will still oxidize the beta-hemes, but at a rate about the same as for the alpha-hemes. Although the spectral changes during the reaction of hydroxylamine with hemoglobin are similar to those when ferricyanide oxidizes hemoglobin, paramagnetic resonance measurements and the relatively small decrease in absorption at 630 nm on adding cyanide to the final product, cast some doubt on whether much of the hemoglobin is oxidized by hydroxylamine.