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Glucagon-like insulinotropic peptide (GLP-1) and its analogs are of interest because of their therapeutic potential in type II diabetes. LY315902 is a GLP-1-(7–37)-OH analog with a modified N-terminus (IP7), an octanoic acid (C8) acylated on the lysine residue at position 34, and a substitution with arginine at position 26. We developed a sensitive and specific radioimmunoassay (RIA) for the determination of immunore-active LY315902 in the plasma of animals. A homobifunctional cross-linker was used to couple the nonacylated form of LY315902 [IP7-R26-GLP-1-(7–37)-OH] to carrier proteins to enhance its immunogenicity. Following immunization, animal antisera were screened by RIA for the presence of LY315902 antibodies. One rabbit produced a high-affinity antiserum that display insignificant cross-reactivity against two forms of native GLP-1 and possible major metabolites of LY315902. In this RIA method …