Acute myelogenous leukemia occurred in a 47-year-old woman whose 25-year history of cutaneous photosensitivity had been undiagnosed until abnormally high erythrocyte, plasma, and fecal protoporphyrin levels were discovered during evaluation for her hematologic disorder. She was found to be heteroallelic for ferrochelatase gene mutations, bearing a novel missense mutation caused by a C185-->G (Pro62-->Arg) transversion in exon 2 of one allele, and a previously described g-->a transition at the +5 position of the exon 1 donor site of the other allele, confirming a diagnosis of erythropoietic protoporphyria. Successful bone marrow transplantation from her brother, who is a mildly affected bearer of the second mutation, resulted in remission of the leukemia and in conversion of the protoporphyria phenotype of the recipient to one resembling that of the donor.