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Different methods of determining the degree of peat decomposition are reviewed, showing fibre content and alkali-extraction as suitable methods. The NaOH extraction technique is tested, with different alkali concentrations, timing, inorganic contaminant and evaporation rates. The results show that the colorimetric measurements of continuous samples can provide a robust and replicable record. Experiments should take into account the inorganic content of peat samples, and keep to a strict time schedule. However, transformation of recorded measurements into the form of percentage humification is questionable, because of the variable nature of humic acids. Data can be best represented as percentage light transmission or optical density. Alkali-extraction of humic acids appear to be more suitable than fibre content in peat-based climatic studies because of the differential response of the latter technique to changing species composition. (48 refs., 3 figs., 2 tabs.)