A progress report. We have helped to standardize an advanced in situ hybridization technology to detect viral nucleic sequences in formalin fixed paraffin embedded brain tissue with high sensitivity and specificity as well as good preservation of cytomorphology. It is our belief that if the inflammation in the multiple sclerosis central nervous system is associated with persistent virus this technique should reveal it. Technical reasons are given why we are continuing to search for measles virus in multiple sclerosis brain tissue.