A new mutant alpha-1-antichymotrypsin (variant ACT) was found by direct sequencing and PCR-single strand conformation polymorphism (PCR-SSCP). This variant ACT was a point mutation of exon V of ACT, with the substitution of Met by Val. Four out of six individuals with this variant ACT had occlusive-cerebrovascular disease, leading to one hypothesis that there might be an association between this mutation and occlusive-cerebrovascular disease.