In the pig species, the preimplanting trophoblast is known to synthesize and secrete high amounts of interferon during early development. Previous experiments in cyclic gilts using total conceptus secretory proteins suggested that porcine trophoblastic interferons, unlike those of ruminants, exert no effect on the luteal cycle. In the present experiment, cyclic Meishan gilts were divided into two groups, cannulated on both uterine horns, and given daily injections of either a placebo or increasing doses of a mixture of recombinant interferon-gamma and interferon-delta, on Days 11-14 of the estrous cycle. In treated gilts, the injected doses were much higher than those previously found in uterine perfusates from pregnant gilts. However, no significant differences could be found between the control (n = 4) and the treated (n = 5) group concerning the days of the estrous cycle for mid-decrease of progesterone (control: Day 14.5 ± 0.57 [mean ± SD]; treated: Day 15 ± 1.25), the day of estrus (control: Day 19 ± 0.96; treated: Day 19.6 ± 0.55), and the subsequent ovulation rate (control: 14 ± 2.2 corpora lutea; treated: 13.1 ± 1.1 corpora lutea). These data confirm that pig trophoblastic interferons, unlike those of ruminants, do not themselves exert an antiluteolytic effect. A possible synergistic effect of embryonic estrogens on the luteal functions of nonpregnant sows remains to be determined.