NY-ESO-1 is a SEREX-defined cancer-testis antigen of which several MHC I, but only few MHC IIrestricted epitopes have been identified. Searching for highly promiscuous MHC IIrestricted peptides that might be suitable as a CD4+ stimulating vaccine for many patients, we used the SYFPEITHI algorithm and identified an NY-ESO-1derived pentadecamer epitope (p134148) that induced specific CD4+ T-cell responses restricted to the HLA-DRB1 subtypes *0101, *0301, *0401, and *0701 that have a cumulative prevalence of 40% in the Caucasian population. The DR restriction of the p134148 pentadecamer was demonstrated by inhibition with an HLA-DR antibody and a functional peptide displacement titration assay with the pan-DR-binding T-helper epitope PADRE as the competitor. The natural processing and presentation of this epitope was demonstrated by recognition of an NY-ESO-1+ melanoma cell line by T cells with specificity for p134148. The pentadecamer p134148 was able to induce CD4+ responses in 4/38 cancer patients tested. However, no strict correlation was found between CD4+ T-cell responses against p134148 reactivity and anti-NY-ESO-1 antibody titers in the serum of patients, suggesting that CD4+ and B-cell responses are regulated independently. In conclusion, p134148 holds promise as a broadly applicable peptide vaccine for patients with NY-ESO-1positive neoplasms.