Trellis Plot Group Variable Font size

I plot a trellis plot in R using the lattice package.  The size of the 
group variable is pretty big (over 100 groups).  I used to do it in 
Splus and the pic there is pretty good.  Now I transfer to R but the 
plot is really not accetable. The group variable font in the R produced 
trellis is so huge that it takes over the major area of the plot.  Any 
one knows how to make the font size smaller?  thanks very much.  best, Alex