We have used a PCR based method to analyze allelic frequencies in a (TG)n(AG)m microsatellite marker located in the first intron of the apolipoprotein C-II gene in French MS patients and controls. Samples were collected from 74 MS patients and from 102 controls. The distribution of microsatellite alleles differed between patients and controls (chi 2 = 7.82), showing a significant effect (P < 0.04) with MS due to the increased frequency of the allele 6 and a decrease frequency (P < 0.03) of allele I. Our study confirms that the apolipoprotein C-II region may influence susceptibility to MS.