A method for determining the total organic carbon in aqueous extracts of humic substances is proposed, by using a CNS automatic analyser: Twenty-Jive NaOH extracts from different organic materials, mainly organic wastes, classified into five groups, were used. The results indicate that the method is easy, rapid, accurate and reproducible. The proposed method was correlated with the traditional Walkley-Black method, and good correlations were found between the two methods for each individual group using both alkali-extractable and fulvic acid fractions together: Also, two equations were obtained for the alkali-extractable and fulvic acid fractions using the 25 materials together Finally, a general equation, including data of the 25 samples and the two fractions, was obtained. Thus the oxidable carbon can be converted into total organic carbon. by the proposed general equation TOC = 1.23 OXC+0.35, with a probability level greater than 99.9%. Copyright (C) 1996 Elsevier Science Ltd.