The distribution of soil organic carbon in a mangrove forest partly contaminated with raw sewage shows that a high proportion of the carbon in the landward zones of the forest was organic. Relative content of inorganic carbon increased seawards. Carbonate from the shells of gastropods, oysters, and corals contribute to the inorganic carbon pool. The vertical profiles of organic carbon showed a general surface enrichment and subsurface depletion. An extremely high organic carbon content up to 19% of sediment (dry weight) was found at the sewage dump site. Peat formation was not evident and the organic carbon content decreased with depth of burial in the sediment. The interstitial water at the terrestrial mangrove fringe with sewage waste was relatively more acidic (pH 4-5) and strongly reducing (Eh - 300 mV). The pH in the terrestrial fringe that had no sewage influence was close to neutral values (pH > 6). There was no significant difference between the rates of organic matter remineralization in the forest zones. Relative values, however, indicate that mineralization was slowest in sewage-contaminated areas compared to areas without exposure to sewage. The rate of remineralization was high in the frequently inundated mangrove areas.