I just started using bioconductor for microarray analysis. First the gpr file was read with marray package, next background was corrected using smida which returns a vector. When the vector was assigned back to marray@maRf, I got an error in checkSlotAssignment. But I can do it element-wise (e.g., marray@maRf[1]<-vector[1], marray@maRf[2]<-vector[2], etc.). YJ Zhang [[alternative HTML version deleted]]