Agranulocytosis was observed in a 63-year-old patient with myelodysplasia 6 weeks after commencing chelation with the oral iron chelator deferiprone (1,2-dimethyl-3-hydroxypyrid-4-one, L1) at a daily dose of 79 mg/kg. Using a liquid culture system no difference was observed when L1 toxicity to normal and patient myelopoiesis was compared (IC50: 150 v 172 microM respectively). L1 was found to be less toxic than desferrioxamine (DFX) (IC50: 150 v 9 microM respectively) to normal myelopoiesis. Delayed addition of iron to myeloid cultures containing an inhibitory concentration of L1 or DFX was associated with reversal of chelator-induced inhibition of myelopoiesis up to 6 h but not after 24 h. Further studies are needed to determine the incidence and elucidate the pathogenesis of agranulocytosis associated with L1 therapy.