The bone morphogenetic proteins (BMPs) constitute a novel subfamily of the transforming growth factor type beta (TGF-beta) supergene family. Here we demonstrate, using polymerase chain reaction (PCR) BMP-4 and BMP-5 messages in RNA isolated from multiple sclerosis (MS) plaque tissue. This is the first demonstration of BMP expression in an inflammatory lesion in general, and in MS in particular. However, BMP-4 and BMP-5 messages could be detected in RNA isolated from a Morbus Creutzfeldt-Jakob (CJD) lesion. Even in normal brain, RNA expression of BMP-4, but not that of BMP-5, was detected. Therefore, BMP-5 gene expression seems to be associated with MS and CJD lesions, whereas the BMP-4 gene appears to be constitutively expressed in the human brain. As TGF-beta s and BMPs are regulators of regenerative processes and contribute to regulation of chemoattraction and local immunoreactivity, BMP-4 and BMP-5 might be involved in aspects of MS lesion formation unknown so far. PCR analysis of human cell lines demonstrate BMP-4 and BMP-5 expression in leukocytic cells, suggesting that infiltrating leukocytes contribute at least in part to BMP-4 and BMP-5 mRNAs of the MS plaque.