THE extent of degradation of natural organic mixtures largely determines their utility as records of depositional history, and their potential to act as nutritional substrates and fossil fuel sources. The degree of decomposition is usually inferred from the physical setting of the deposits(1) or from bulk chemical composition(2), but in both these cases the interpretation can bk obscured by several factors(3). We report here a study of aldoses and amino acids in samples collected from a variety of marine depositional environments and representing widely different stages of alteration. We identify consistent trends in three compositional characteristics : the percentage of organic carbon in the form of aldoses and protein amino acids, the percentage of total nitrogen present as protein amino acids, and the percentage of total amino acids present as beta-alanine and gamma-aminobutyric acid. Each of these parameters is sensitive to a different stage of alteration, and they appear to be uncompromised by source variations. Applied together, they offer concordant information on the relative diagenetic stage and reaction potential of natural organic mixtures under both aerobic and anaerobic depositional conditions.