Those interested in the issue of BrdU labeling for proliferating cells will
find this paper very informative.  One quote: "...neither single nor
repeated daily injections of BUdR accurately measure 'proliferation'."
Accurate measurement of proliferation variables is apparently far from
trivial.

Brain Res Dev Brain Res 2002 Mar 31;134(1-2):77-85  Dynamics of cell
proliferation in the adult dentate gyrus of two inbred strains of mice.
Hayes NL, Nowakowski RS.
http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list
_uids=11947938&dopt=Abstract
Mike King
UF Neuroscience
Gainesville FL