Somatostatin (SRIF) is known to have inhibitory effects in a wide variety of tissues but a role in reproduction has not been described. The present studies describe the influence of SRIF immuno-neutralization on the reproductive performance of sheep and pigs. In experiment 1, Rambouillet × Suffolk ewe lambs were actively immunized against SRIF conjugated to ovalbumin (SI; n = 24) or were not immunized (CT; n = 32). Primary immunizations were initiated at weaning and boosters given at 4-week intervals, as well 10 days before breeding and lambing. Over two years, breeding periods were September and January (in-season) and May (out-of-season). Pregnancy rates were higher for SI than for CT ewes following both in-season (P < 0.01) and out-of season breeding (P < 0.06). The number of lambs born per ewe lambing was not affected by treatment. In experiment 2, Yorkshire × Landrace gilts were actively immunized against SRIF-ovalbumin conjugate (n = 37) or were not immunized (n = 38). Primary immunizations were given at 39.8 ± 1.5 kg body weight and boosters after 4 weeks, 10 days before breeding and at 105 days of gestation. Some SI (n = 15) and CT gilts (n = 17) were slaughtered 10 days after estrus to determine ovulation rates. Remaining SI (n = 22) and CT (n = 21) gilts carried their litters to term. Ovulation rates tended to be higher (P < 0.1) in SI than CT gilts (11.8 ± 0.6 vs. 10.7 ± 0.4). There was no effect of treatment on pregnancy rates to initial breeding (86.4 vs. 90.5% for SI and CT gilts, respectively) but first litter size tended to be larger (P < 0.07) for SI than for CT gilts (9.95 ± 0.34 vs. 9.00 ± 0.38). There was no effect of treatment on litter growth performance during lactation. These data provide evidence that SRIF may be involved in the regulation of reproduction.