In the combination dose-ranging study, 4 groups of 3 patients are randomly assigned to 1 of 2 doses of tin mesoporphyrin. After a 4-12 week washout, these patients are crossed to a standard or low-dose heme arginate infusion. After a second 4-12 week washout, patients are given a combination infusion of tin mesoporphyrin followed by heme arginate.