[BioC] merging two sets of genes

[kfbargad@ehu.es]

Dear list,

I have two sets of genes from the same experiment,

> PinC
Expression Set (exprSet) with 
        1310 genes
        8 samples
                 phenoData object with 2 variables and 8 cases
         varLabels
                FileName: read from file
                Target: read from file
> PinS
Expression Set (exprSet) with 
        2891 genes
        8 samples
                 phenoData object with 2 variables and 8 cases
         varLabels
                FileName: read from file
                Target: read from file


How can I merge these two sets? I tried union() on two vectors created 
from the probe IDs but failed. Any hints?

thanks in advance,

David