The region surrounding the myelin oligodendrocyte glycoprotein (MOG) gene, located telomeric to the major histocompatibility complex on chromosome 6, was shown to contain three highly informative microsatellites. To examine the potential role of variants of the MOG gene in susceptibility to multiple sclerosis, these CA-repeat polymorphic markers were characterized on a sample of 169 multiple sclerosis patients and 173 healthy unrelated individuals by a method combining fluorescence labelling of PCR products and use of an automated DNA sequencer. Both patients and controls lived in the southwest of France (in the Pyrénées-Atlantiques) and had similar ethnic background. The distribution of the MOG haplotypes was not significantly different in the two groups (P = 0.38). This is not in favour of the implication of the MOG gene in the genetic component of multiple sclerosis, unless different independent mutations have occurred within this gene.