A dimer of CKS-17 has a natural occurring cysteine at the carboxyl terminus (where it occurs in the retroviral peptides on which CKS-17 is based) and dimerization is accomplished by cysteine-disulfide linkage. CKS-17 is a synthetic retroviral envelope heptadecapeptide corresponding to a region highly conserved in retroviral transmembrane proteins such as pl5E. The CKS-17 peptide has been previously shown to inhibit monocyte superoxide production, natural killer cell activity, polyclonal B-cell activation, and monocyte-mediated killing by inactivation of interleukin-1.