The tannins extractable from new and aged leathers in a water/acetone solution (1/1, v/v), were measured by high-performance liquid chromatography (HPLC) and expressed as the integrated absorption of all tannin peaks at 280 nm, or as gallic acid equivalents per 100 mg of dry leather. Colorimetric analysis of the extracts for the presernc of phenolic substances was given as an amount of gallic acid equivalents per 100 mg of dry leather. These analytical data showed that the tannin content of leathers without the need for other analyses; also, the tannin type (hydrolysable or condensed) does not have to be determined for new leathers. Parameters such as the HPLC elution profile, the spectral characterisation of individual peaks or fractions, and the calculation of the relative abundance of ellagic acid, protocatechuic acid and other small molecules were combined to identify the tannin types of historical leathers. The changes in the tannin profile brought about by both artificial and natural ageing of leather were also evaluated. -- CAL