Hi I have been using a bit of namespaces in the past, but the following alludes me. I am dealing with the Bioconductor packages Biobase and affy. Biobase has a namespace and affy does not. affy contains the S4 class "AffyBatch" which extends the "eSet" class in Biobase. I am extending the AffyBatch class myself. My code works fine as long as I do not have any NAMESPACE file. Now I am trying to add one. I am importing Biobase, but I cannot import affy since it does not have a NAMESPACE. However, when I try R CMD INSTALL it complains that it cannot find AffyBatch : Error in setIs(Class, class2, classDef = classDef, where = where) : Unable to find package environment for class "AffyBatch" to revise subclass information So how do I make the classes in affy available for my package when affy does not have a NAMESPACE? The relevant lines from my DESCRIPTION file is Depends: R (>= 2.6), affy (>= 1.16), affxparser (>= 1.10), Biobase, methods LazyLoad: yes and from my NAMESPACE file I have exportPattern("^[^\\.]") import(Biobase) I have also tried (in desperation) to add a "require(affy)" in both .onLoad and .onAttach, but to no help. While I am at this: as I remember it, in the old days we needed "require(methods)" in .onLoad to work with S4, is that still necessary? I am using R-2.6.0 on OS X (PPC) Thanks, Kasper