Serum cortisol and immunoglobulin G (IgG) concentrations were measured to investigate the relationship between vitamin A status and immune function in lambs. Twenty-four crossbred ewe lambs were each fed 900 g·d-1 of a carotene—deficient diet composed of 95.5% whole oats, 3% molasses, .5% trace mineral salt and 1% limestone. All lambs were injected monthly with vitamins D and E and with selenium. The 12 control lambs also received a 100,000 IU oral dose of vitamin A palmitate in capsule form every 2 wk. All lambs were challenged by injecting them with 1 mg ovalbumin in 1 ml of Freund’s complete adjuvant. At the time of challenge, serum vitamin A levels for the control and A-deficient (A—def) lambs were 33.3 and 3.1 ug·dl-1 respectively. Blood was collected prior to and 6, 13, 20 and 34 d post—challenge. The lambs were then reschallenged using the same antigen and blood was obtained 1, 2, 6 and 22 d post—challenge. Lambs were sacrificed at the end of the second challenge period. Spleen weights were obtained and gross post—mortem observations were made at this time. / Master of Science