beta-Glucuronidase is one of the most important hydrolytic enzymes in living systems and plays an essential role in the detoxification pathway of toxic materials incorporated into the metabolism. Some organs, especially liver and some tumour tissues, have high level of beta-glucuronidase activity. As a result the enzymatic activity of some kind of tumour cells, the radiolabelled glucuronide conjugates of cytotoxic, as well as radiotoxic compounds have potentially very valuable diagnostic and therapeutic applications in cancer research. For this reason, a sensitive measurement of beta-glucuronidase levels in normal and tumour tissues is a very important step for these kinds of applications. According to the classical measurement method of beta-glucuronidase activity, in general, the quantity of phenolphthalein liberated from its glucuronide conjugate, i.e. phenolphthalein-glucuronide, by beta-glucuronidase has been measured by use of the spectrophotometric technique. The lower detection limit of phenolphthalein by the spectrophotometric technique is about 1-3 mug. This means that the beta-glucuronidase levels could not be detected in biological samples having lower levels of p-glucuronidase activity and therefore the applications of the spectrophotometric technique in cancer research are very seriously limited. Starting from this consideration, we recently attempted to develop a new nuclear technique to measure much lower concentrations of beta-glucuronidase in biological samples. To improve the detection limit, phenolphthalein-glucuronide and also phenyl-N-glucuronide were radioiodinated with I-131 and their radioactivity was measured by use of the counting technique. Therefore, the quantity of phenolphthalein or aniline radioiodinated with 1311 and liberated by the deglucuronidation reactivity of beta-glucuronidase was used in an attempt to measure levels lower than the spectrophotometric measurement technique. The results obtained clearly verified that 0.01 pg level of phenolphthalein or aniline could easily be detected at least 106 times more sensitively. The preliminary results obtained on some biological samples have shown that beta-glucuronidase levels could reasonably be measured by use of the nuclear technique. In addition, our results also indicate the potential application of the radiolabelling technique to measure very low beta-glucuronidase levels in different biological samples in cancer research and other related fields. The objective of our study is to demonstrate the potential application of the nuclear measurement technique in different biological samples.