['The objective was to examine effects of gonadal hormone manipulation on aortic diameter and macrophage infiltration in rodents during abdominal aortic aneurysm (AAA) formation.', 'Experiment 1: 17-beta estradiol and testosterone pellets were implanted in male (ME) and female (FT) rats. No pellet was implanted in shams (MES, FTS). Experiment 2: Testes and ovaries were removed from males (MO) and females (FO), respectively. No organs were removed from shams (MOS, FOS). Experiment 3: Male and female rats were orchiectomized and oophorectomized, respectively. Four weeks post-castration, testosterone (MOT) and 17-beta estradiol (FOE) pellets were implanted. Shams underwent castration, but no pellet was implanted (MOTS, FOES). All rats underwent infrarenal aortic infusion with elastase postimplantation/postcastration. Diameters were measured on postoperative d 14. Tissue was stained for macrophages by immunohistochemistry.', 'Diameter (P = 0.046) and macrophage counts (P = 0.014) decreased in ME compared with shams, but not in females treated with testosterone (FT). Diameter (P = 0.019) and macrophage infiltration (P = 0.024) decreased in MO compared with shams, but not in FO. Diameter increased in MOT compared with MOTS (P = 0.033), but decreased in FOE compared with FOES (P = 0.002). Macrophages decreased in FOE compared with FOES (P = 0.002).'] Is differential regulation of aortic growth in male and female rodents associated with AAA development?