The use of an electrolytic respirometer for characterization of chemical compounds and wastewater was studied. From the BOD curves generated by the respirometer, the first order biokinetic constant (K), ultimate BOD (BODu) and adaptation period were estimated. The estimated ultimate BOD values of the known chemical compounds were very close to the theoretical oxygen demand values. Using K values, the relative biodegradability of the chemicals could be compared while the adaptation period for each compound could vary with the type of seed micro-organisms used. It was found that BOD5 values determined by the conventional method have no or very little, if any, meaning as far as the biological characteristics of industrial wastewaters are concerned. The BOD curves for wastewaters consisting of 2 or 3 different compounds could be divided into several stages while those for the combined wastewaters could be expressed as one curve.