Has the add parameter of plot commands been deprecated?

R for OS X, version 2.0.1

Has the add parameter of plot commands been deprecated?  It no longer 
occurs in the help listing for plot, and doesn't work, either.  If it 
has been deprecated, what is the replacement?  That is, how does one 
overlay an existing plot?
--
John R. Vokey, PhD
Professor
B.E.R.G. - Behaviour and Evolution Research Group
Micro-Cognition Laboratory
Department of Psychology & Neuroscience
University of Lethbridge
Lethbridge, Alberta T1K 3M4
CANADA