Hi All The platform for GSE4137 is "Custom cDNA 41,424 clones", and organism is human. I tried the code which you mentioned,but gives me error:- get("AA502230",revmap(org.Hs.egACCNUM)) Error in .checkKeys(value, Rkeys(x), x at ifnotfound) : value for "AA502230" not found Is this error coming becuase i am using it for cDNA platform? Regards