Employing a continuous bile collection, we measured the bile secretion of porphyrins, haem (iron protoporphyrin IX regardless of oxidation state) and bilirubin in five healthy subjects. The baseline values for the flow of porphyrins in the bile were: 4.7 +/- 1.9 nmol/h uroporphyrin, 27.3 +/- 3.8 nmol/h coproporphyrin and 39.2 +/- 11.7 nmol/h protoporphyrin. Bile haem flow was 59.7 +/- 12.6 nmol/h, and that of bilirubin 23.8 +/- 8.2 mumol/h. Following haem injection (6.4 mumol/kg) the flow of protoporphyrin but not of the other porphyrins was reduced, and the bile haem flow increased (232 +/- 109.5 nmol/h), while the flow of bilirubin did not increase significantly. A few patients with representative porphyrias showed the expected increase in copro- and protoporphyrin in the bile. The patient with coproporphyria exhibited a bile flow of coproporphyrin of 1470 +/- 133 nmol/h and of protoporphyrin of 334 +/- 29 nmol/h; haem infusion significantly reduced the bile flow of both porphyrins (to 649 +/- 101 for copro- and 215 +/- 36 nmol/for protoporphyrin). The patient with protoporphyria had an increased protoporphyrin flow, yet haem infusion caused no reduction in protoporphyrin flow (106 +/- 7 after v. 81.4 +/- 13 nmol/h before haem). In conclusion, we found that haem and porphyrins are normal constituents of bile, and that injected haem appears in bile. Bile bilirubin did not rise within 12 h after haem infusion a finding which warrants further investigation.