Myoglobin, which is located in muscle cells, serves as a reserve supply of oxygen for muscle functioning. This molecule consists of a single globin unit (MW ≈ 16,700 Da) with just one oxygen binding site. In contrast to hemoglobin, myoglobin will absorb or release an molecule at a much lower partial pressure. The skeletal muscles of aquatic mammals, such as whales and dolphins, are particularly rich in myoglobin, which allows them to be submerged for long periods of time.

A phenomenon known as the Bohr effect was discovered in 1904 by Danish physiologist Christian Bohr (father of physicist Niels Bohr). This constitutes a reduction in the oxygen affinity of hemoglobin as blood acidity increases, with pH decreasing from its normal value of 7.4, usually as a consequence of an increase of concentration in the blood. Myoglobin does not exhibit the Bohr effect.

This Demonstration plots the dependence of oxygen saturation on and pH. The average number of bound molecules is shown in the top illustrations. These are highly schematic, with the molecules being greatly magnified.