Red cells from 6 convalescent hospital patients without evidence of porphyria and from 2 patients with erythropoietic porphyria (5 studies) were incubated with delta amino laevulinic acid (ALA) thereby increasing the intracellular porphyrin concentration. These cells were then labelled with 3H DFP or DF32P and re‐injected, and their life‐span compared to a control population of cells labelled with the alternate isotope. Increasing the cellular porphyrin concentration did not alter red cell life‐span. Similarly, increasing the level of porphyrins in rabbit whole blood did not diminish their life‐span, when measured with radiochromium. These data indicate that increased intracellular porphyrin concentration does not prejudice red cell life‐span, and that the haemolytic anaemia in patients with erythropoietic porphyria is not due to the increased intracellular porphyrin concentration.