Association between narcolepsy and HLA-DR2 antigen is the strongest so far described between an HLA antigen and a disease. Among 28 narcoleptic patients, we found two HLA-DR2 negative cases: a caucasoid woman also suffering from dystrophia myotonica and a negroid. All of our patients were HLA-DQW1 positive. An hypothetical narcolepsy susceptibility gene could be located in the HLA region, closer to the DQ than to the DR gene. It could be a pathologic allele of a sleep controlling gene in linkage disequilibrium with DQW1. Presence of DQW1 is a quasi-requisite for the expression of narcolepsy. It is not sufficient as it is observed in 70 p. 100 of controls.