The chemical nature and extent of contaminants were studied in fifty-five charcoals covering a wide range of age, origin, and environment, especially those buried in soils and archaeo-logical deposits. Contaminants removed with an alkali-pyrophosphate mixture (0.1M Na₄P₂O₇, 0.1M NaOH) were mostly absent in laboratory charcoals but ranged 2-100% in all other charcoals studied. However, most of the buried charcoals examined contained less than 50% extractable carbon. The alkali-pyrophosphate treatment thus removed equal to or less than 50% of the total oxidizable organic carbon, which in turn accounted for less than 50% of the total carbon in buried charcoal, leaving enough residual carbon for radiocarbon dating. On the average, more humic acid than fulvic acid was found in the extractable carbon fraction. IR data confirm that both contaminants in buried charcoals were derived from adsorbed soil humic substances. On the other hand, absorption bands typical of soil humic substances were absent in spectra of charcoals which had been treated with alkali-pyrophosphate. -- AATA