Roche AMPLICOR HCV PCR

[GERALDINE KAMINSKI]

Is anyone using the AMPLICOR Hepatitis C PCR kit from Roche having
problems with their positive controls?  We use a lot of this product
and often find the positivity of the controls provided tail off
with time (about 2-3 weeks).  Recently the positive control was 
completely negative each time it was tested ( 9 times in all).
I'm not sure how much of this is due to our technique ( we've been using
it since 1994). I do know some other labs have reported problems although
I don't know how widespread this is.
I'd be grateful for any comments from other users.