Abstract
A rapid and reliable autoradiographic technique for plaque-forming cells (PFCs) using (14)C rather than tritiated thymidine is described. Its application to PFCs developing in vitro shows that (a) practically all PFCs derive from precursors dividing steadily during the culture period, (b) PFC precursors divide in the absence of T-cell helper function, and (c) at least some PFCs may continue to divide.