The effects of levamisole, as an anthelmintic or immunomodulator, on pregnancy were investigated in ewes. Immunomodulatory and anthelmintic doses of levamisole and physiologic saline were injected on days 0 (oestrus), 7, 14, and 21 in group I (immunomodulatory dose; n=7), group II (anthelmintic dose; n=6), and group III (control; n=6), respectively. The first service pregnancy rate, tended to be lower (P<0.06) in group I (28.6%) compared to that of groups II (83.3%) and III (83.3%). Plasma progesterone (P-4) concentration was significantly higher (P<0.05) in group II compared to that of group III on day 3, and there was a treatment x day interaction (P<0.05). No effect of levamisole treatments on plasma P-4 concentrations was detected once pregnancy was established. There was a numeric decline in plasma cholesterol concentrations in group II, compared to group I or III on day 3. In conclusion, levamisole as an immunomodulator is detrimental for the establishment of pregnancy, possibly by stimulating general and intrauterine immunity.