Termination of tritiated thymidine incorporation by freezing the cells.

It is often desirable to be able to stop the uptake of tritiated thymidine by a number of transforming lymphocyte cultures at a specific time. This is important for kinetic studies but may be difficult if the number of cultures to be harvested at one time is large. We describe in this report a simple method to stop the incorporation of tritiated thymidine into any number of transforming lymphocyte cultures simultaneously.