To combine the advantages of solid scintillation and the use of 96-well plates, an in-plate cell proliferation assay was designed using scintillation wax. Messy, conventional liquid wastes are not produced, thereby making solid scintillation safer and more convenient. Additionally, the use of optimized, 96-well ViewPlates for inplate counting procedures allows the monitoring of cell morphology during the course of the stimulation experiment. The scintillation wax, FlexiScint, was used for counting [3H]thymidine incorporation in an adherent cell line and compared to liquid scintillation counting. The data presented here demonstrate that this new assay produces results comparable to those obtained by conventional methods.