“…However, refractory states observed in guinea-pigs after repeated bioassays of the hormone (Noall & Frieden, 1956;Frieden, 1958) and reports of localized transient chills or pain (Perkoff, Salhanick, Zarrow, Nelson & Tyler, 1954;Kelly & Posse, 1956;Eichner, Waltner, Goodman & Post, 1956) and anaphylactic reactions (Evans, 1959;Wendt & Wolfe, 1959) in the clinical literature indicated that an antibody to relaxin might be produced. The formation of a relaxin antibody in rabbits was first reported by Cohen (Cohen, 1963;Cohen & Graff, 1963). This study confirms the ability of relaxin to induce antibody formation in the rabbit and presents data on the biological and immunological characteristics of the antibody.…”