[R] About print a label in plot

[affy snp]

Dear list,

Hello! I have a question about how to print a label in the plot.
I am using the following code:

<pdf("mel4_chr3_11cancer_cghFLasso.pdf", height=6,
width=5);plot(Disease.FL, index=i, type="Single",main="Plot of
Labels");dev.off();

But "Plot of Labels" has not been printed. Any suggestions?

Thanks a lot!
      Allen