In an attempt to quantify iron and aluminium removal in patients following desferrioxamine therapy, a comparative study of haemodialysis and haemofiltration was performed in five patients. Haemofiltration was found to be the more efficient treatment especially if iron and aluminium clearances were related to urea clearances. The distribution volumes of chelated iron and aluminium at the low clearance rates obtained, behave as a single compartment which amounts to about 40 per cent of body weight.