Abstract Neisseria meningitidis strains A1 and M978 both express the lipooligosaccharide (LOS) L8 immunotype [Gu et al., J. Clin. Microbiol. 30 (1992) 2047–2053]. Under different growth conditions, strain A1 did not change its LOS profile whereas strain M978 produced variable LOS profiles on SDS–PAGE. To understand the genetic basis of LOS conservation and variation, their lgt locus encoding glycosyltransferases responsible for the biosynthesis of the α-chain of LOS was analyzed. Strain A1 possessed only two genes, lgtA and lgtH, at the lgt locus. The lgtA gene was inactivated due to a frameshift mutation; thus strain A1 expressed only L8 LOS. In contrast, strain M978 contained five genes lgtZ, lgtC, lgtA, lgtB and lgtE at this locus, thus it had a potential to express L1, L3,7 in addition to the L8 LOS. The data showed that strain A1 is a better reference strain for the L8 immunotype because of the stability of L8 LOS expression resulting from its unique lgt locus. In addition, these two strains had two new genetic organizations, lgtAH and lgtZCABE, compared to the reported gene organization at the lgt locus in N. meningitidis.