Although there are excellent clinical results from using cerium nitrate plus silver sulphadiazine in the treatment of deep dermal burns in our burn centre, its mechanism of action remains unexplained. We set up a prospective study to establish a hypothesis which could explain the formation of the typical leathery crust. Burns treated with cerium nitrate plus silver sulphadiazine and silver sulphadiazine alone were compared histologically and metallurgically. Application of cerium nitrate plus silver sulphadiazine on deep dermal burns caused superficial connective tissue calcification with few deep dermal changes. Cerium penetration was low and silver was never detected intradermally. The precipitation of cerium and pyrophosphate destroys the calcification inhibitory function of the latter, creates multiple calcification nuclei and leads to superficial dermal calcification. No calcium was detectable in biopsies from silver sulphadiazine-treated wounds. No major toxicological side-effects were seen during this study. The clinical results were favourable, as have been reported previously.