Background: There is considerable Oepidemiological evidence that a latent or slow infection with human herpes virus 6 is associated with the etiology of multiple sclerosis. However, techniques for detecting anti-human herpes virus 6 antibodies in the cerebrospinal fluid had been lacking up to the time of this study. Preliminary results were presented at the Second International Conference on Human Herpesviruses 6, 7 and 8 (Italy, Pisa, May 8-11, 1997). Methods: We therefore adapted the enzyme-linked immunosorbent assay in order to make this determination.