Hemin has a profound effect on erythroid cell maturation and promotes fetal hemoglobin synthesis in vitro. In β-thalassemia, increasing fetal hemoglobin levels can ameliorate the anemia. We administered heme arginate, a novel stable form of hemin, to 4 patients with thalassemia intermedia and studied the in vitro versus in vivo effects. In erythroid cultures, there was a marked rise in total hemoglobin and hemoglobin F. In vivo, 3 of 4 patients had a rise in hemoglobin levels (from 0.4 to 1.1 g%), which was statistically significant in 1 patient. There were no serious adverse effects. Heme arginate may be useful in the treatment of thalassemia intermedia.