The aim of this study was to determine the effectiveness of intramuscular injections of beta-carotene (beta C) and GnRH on luteal size (LS), luteal blood flow (LBF) and serum beta C concentrations in early pregnant cows. Twenty-nine Holstein-Friesian cows with a mature corpus luteum (>19mm) were randomly assigned to two groups: pc not received (beta C-; n=15) or received (beta C-; n=14). All cows were treated with PGF(2)alpha and inseminated twice, 48 and 72h after the treatment. Last Al was considered to be day 0. All cows received GnRH on day inseminations, 7 and 17. Different from the beta C-, the beta C+ group received beta C intramuscularly on day 7 and 17. In both groups, measurement of LS and LBF were performed on days 7, 10, 17,27 and 37 by transrectal B-mode and colour Doppler ultrasonography. Blood samples were collected on each examination day. Only cows that became pregnant were included in the statistical evaluation. The concentration o beta C in the beta C+ group was higher than in the beta C- at all examination days except day 17 (P<0.05). There was no significant difference between groups concerning the progesterone concentrations (P>0.05). The LS and LBF of beta C+ group on day 7 (P<0.05) and 27 (P<0.01) was higher than in the beta C- group and values increased significantly until day 37 (LS: P<0.05, LBF: P<0.01). We conclude that beta C injections significantly increased serum beta C concentrations, as well as LS and LBF.