We report the successful treatment of the syndrome of pigmentary dilution and immunodeficiency (Griscelli's syndrome) with allogeneic bone marrow transplantation. Griscelli's syndrome includes silvery hair, recurrent infections, hepatosplenomegaly, progressive neurologic deterioration, and lymphohistiocytosis and is uniformly fatal. We present a family in which four of seven children of consanguinous parents were affected. The affected children were all born with silvery hair. Microscopic examination of the hair showed large clumps of pigment in the hair shaft. Skin biopsy revealed an accumulation of melanosomes in the melanocytes. Three of the affected children were deceased before 20 months of age. Pathology of liver and lung in two of the siblings showed an infiltration of lymphocytes and histiocytes. Immunologic studies in one of these cases were notable for a decreased number of T cells and poor T-cell mitogen stimulation with concanavalin A (Con A) and pokeweed mitogen (PWM). Recently, a fourth sibling with silvery gray hair was referred to us at 3 months of age for evaluation. T-cell function studies were normal and she appeared in overall good health. Because of the expected fatal outcome, allogeneic bone marrow transplantation was performed at 4 months of age. Two years later the patient remains in excellent health. This suggests that cells of hematopoietic origin are responsible for the fatal outcome in Griscelli's syndrome and that bone marrow transplantation early in the course of the disease is an important modality for treatment of this syndrome.