The dynamics of conjugation of 14C-bilirubin injected intravenously during cholestasis is known from studies in rats and dogs. No studies have been performed concerning the conjugation of non-erythroid bilirbuin (NEB), i.e. the 10-20% of bilirubin synthesized from tissue haemes, mainly in the liver. This study reports the results of experiments in four dogs subjected to extra-hepatic cholestasis of 7-14 days' duration. delta-Aminolevulinic acid-5-C14HCi was injected intravenously as a NEB precursor. The appearances of unconjugated and conjugated labelled NEB as well as of the different azopigments were followed in systemic blood, liver vein blood, and thoracic duct lymph. The first NEB to appear was unconjugated; maximal concentration of unconjugated NEB in peripheral and liver vein blood was reached within one hour. The amount of conjugated NEB in both vascular compartments increased for two to three hours, after which time the degree of conjugation stabilized. The degree of conjugation was higher in liver vein than in peripheral blood for the first two hours. The same azopigments of NEB were found as for injected 14C-bilirubin. The a0 azopigment (azobilirubin) was present in higher amounts in peripheral than in liver vein blood, all the other azopigments were present in higher amounts in liver vein blood.