Isoelectric focusing (IEF) across an urea gradient, and titration curves obtained by IEF—electrophoresis with and without urea, were used to characterize porcine and bovine haemoglobin and globins prepared either by the cold-acetone method (native globin) or by a new method based on haem precipitation with a dilute carboxymethylcellulose (CMC) solution of acidic pH. CMC-treated bovine globins dissociated at moderately low urea concentration into α and β subunits. In native bovine globin and in CMC-treated porcine globin, one intense band consisting of both α and β subunits was stable to urea at the isoelectric point (pI), but was dissociated into subunits below the pI. Common to all titration curves of the globins was a marked reduction in mobility at pH below 5.0 in the case of bovine globin and below 6.0 in the case of porcine globin because of the formation of an aggregate. In all globin samples except spray-dried bovine globin the main brand remained stable between the pI and the pH of aggregation.