Abstract: The present invention provides a test sample container for measuring the biological activity of cells, bacteria, or micro-organisms in a test sample by radiometric techniques. The container is suited for use with automated laboratory equipment and provides greatly improved measurement efficiency over prior designs. In one embodiment, the test sample container includes a serum vial adapted to contain a quantity of a test sample and a radionuclide-labeled nutrient media. A micro-tube, which contains a mixture of a gas absorber and a scintillation compound, is positioned above the surface of the sample/media mix by a split-skirt stopper that also serves to seal the serum vial. The gas metabolized or otherwise evolved by the micro-organisms in the test sample is absorbed by the absorber in the micro-tube causing the scintillation compound to emit light flashes at a rate proportional to the quantity of radioactive gas absorbed.