The adjuvant activity of the peptide corresponding to the fragment 163-171 of human interleukin 1 beta (VQGEESNDK) has been evaluated on the immune response to both T-dependent and T-independent antigens. The hydrochloride derivative of the peptide showed an effect quantitatively comparable in molar terms to that of the entire protein. At variance with the entire IL 1 protein the peptide appeared devoid of inflammatory effects and therefore it may find clinical applications as adjuvant for poorly immunogenic vaccines or as immunorestorative agent. The activity of other fragments in proximity of the sequence 163-171 was also evaluated. The shorter fragment 165-171 appeared as active as the 163-171 peptide.