The metabolic fate of heparan N-[(35)S]sulphate was studied in rats. Heparan sulphate was obtained from either bovine aorta or lung and labelled with (35)S by desulphation and subsequent resulphation in vitro. Experiments in which heparan N-[(35)S]sulphate was administered intravenously to either free-range or wholly anaesthetized rats with ureter cannulae established that substantial desulphation occurs in vivo, with elimination of inorganic [(35)S]sulphate in urine. Oligosaccharides labelled with (35)S, possible intermediates in heparan sulphate degradation, could not be detected in urine or blood. The general distribution of radioactivity after administration of heparan N-[(35)S]sulphate, as demonstrated by whole-body radioautography, suggested that desulphation was not restricted to one organ in particular. Support for this view was obtained in experiments in which heparan N-[(35)S]sulphate was administered to animals after the removal of kidneys, liver, spleen, pancreas or gastrointestinal tract. In all cases inorganic [(35)S]sulphate was still produced. The ability of rats of desulphate heparan N-[(35)S]sulphate was progressively impaired by increasing concentrations of heparin administered simultaneously. It was concluded that heparan sulphate is metabolized at a number of sites in the body by a sequence of degradative events leading to the formation of inorganic sulphate. It is also concluded that at least some of these events are common to heparan sulphate and heparin.