A novel biodegradation test using Biolog MT microplates was developed. The method was based on the reduction of Tetrazolium Violet during mineralization of organic substrates. Both a microbial mixed culture (activated sludge) and pure culture of a bacterium (Pseudomonas aeruginosa) were used as inocula to evaluate its applicability. The procedure was successfully demonstrated with the ozonated samples of p-nitrophenol. Compared with previous methods, the proposed method is fast and convenient to use in practice.