In the present study, we investigated the influence of HLA class I and class II genes in the response to interferon-beta (IFNbeta) in multiple sclerosis (MS) patients. HLA-A, -B, -C, -DRB1, -DQA1, and -DQB1 DNA typing was performed by polymerase chain reaction-sequence-specific oligonucleotide (PCR-SSO) in a cohort of 149 relapsing-remitting MS patients classified into IFNbeta responders (n=74) and non-responders (n=75) based on stringent clinical criteria. Distribution of HLA class I and class II alleles individually and the HLA-DR2 haplotype was similar between responders and non-responders to treatment. These findings do not support a role of the HLA class I and class II genes as modifiers of the response to IFNbeta.