This paper describes separate spectrophotometric procedures for rapidly measuring carboxyhemoglobin (COHb) and methemoglobin (MetHb) in blood. Absorbance measurements are made in the Soret region at a blood dilution near 1000-fold. For COHb estimation, the diluent contains sodium hydrosulfite, providing the two-component system COHb--Hb for absorbance measurements at 420 and 432 nm. The NA2S2O4 effectively prevents dissociation of COHb by oxygen. For MetHb estimation, the diluent contains KCN and carbon monoxide, providing the two-component system COHb--CNMetHb. Absorbance measurements are made at 420 nm, before and after addiely analyzed for the total of all MetHb forms present. Each procedure requires about 3 muL of blood and can be applied to human or animal blood. Results obtained by the present methods are in satisfactory agreement with currently accepted procedures, which require much larger samples or more elaborate equipment.