BrDU proliferation assay

[chris at austin.unimelb.edu.au]

Has anyone had experience with the BrDU labelling assay
for cell proliferation?  I have attempted to use it in 
a manner analagous to the continuous labelling of cells
with tritiated thymidine.  This a simple method giving
much information of cell cycle time etc.  However, 
rather than getting a simple increase in labelling over
time with an eventual plateau when all cells are 
labelled, I obtained a sine curve with two peaks, the 
second less than the first.  I would be glad of any 
explanations (or even half convincing fictions!).

Thanks in advance,
Chris Bradley