Single strand conformation analysis has become the most widely used technique to screen large numbers of DNA samples for unknown mutations which may contribute to genetic susceptibility to disease. The method relies on the electrophoretic migration of a single strand of nucleic acid in a polyacrylamide gel being dependent on its conformation which is in turn dependent on its sequence. We have examined two closely related genes present in the first intron of the neurofibromatosis type I gene--the oligodendrocyte myelin glycoprotein (OMGP) gene and the ecotropic viral integration 2A (EVI2A) gene--in 36 patients with multiple sclerosis (MS) and 36 healthy controls. A single mutation was found in the OMGP gene which resulted in an amino-acid change of glycine to aspartic acid. This occurred in identical proportions (16.6%) in MS patients and controls. Two rare mutations were found in the EVI2A gene, one resulting in an arginine substituting for a glutamine (one control and one patient), the other in the replacement of a glycine with serine (one control only). A third common polymorphism was seen in 5'-untranslated region of the EVI2A gene, with 65% of patients and controls showing a T-->C transition in either a heterozygous or a homozygous form. This makes it unlikely that either of these genes is involved in genetic susceptibility to MS, but regions of these genes outside of the exonic sequences have not been examined.