Couldn't find the thread, but I remember a huge discussion about mutations in viral thymidine kinase vs lack of viral thymidine kinase. I was happy to just go with what's in FA14 (acyclovir==mutation, ganciclovir==either), but Lange Pharmcards says acyclovir resistance due to lack of thymidine kinase. I didn't think this was a big deal until reading that thread sometime last year.. Was there ever any resolution? I remember @Phloston having a pretty good explanation.