[14C]Thymidine uptake into V-79 hamster lung fibroblasts has been successfully demonstrated using a noninvasive, real-time method utilizing Cytostar-T scintillating microplates. These plates are standard format, tissue culture-treated, 96-well microplates with an integral scintillating base. The microplates permit the culture and observation of adherent cell monolayers. Biological activities of the cells can be studied by the provision of specific radiolabeled compounds. The biological activities of the adherent monolayer bring the specific radiolabel into proximity with the scintillating base and a scintillation signal is thereby generated. [14C]Thymidine incorporation on the microplates can be used to examine cell proliferation and cell cycle events. Using a combined mitotic shake-off/aphidicolin treatment to achieve synchronization, the thymidine incorporation activities of V-79 cells have been examined on Cytostar-T plates and correlated to traditional methods of determining incorporation. The method was further used to examine the effects of colcemid and olomoucine, both chemical inhibitors of cell proliferation, on synchronous populations of cells. The homogeneous detection format and the microplate nature of the method suggest a role for scintillating microplates in cell biology research and drug discovery.