Summary The distribution of bilirubin between albumin and mitochondria suspended in isotonic aqueous media was investigated between the range of 6.5-7.4. It was found that more bilirubin is associated with the mitochondrial phase as the hydrogen ion concentration of the medium increased. Salicylate was additive to the influence of pH on bilirubin distribution, and the combined effects of salicylate and pH 6.5 displaced bilirubin from albumin even at molar ratios of bilirubin to albumin less than one.