The objective of this study was to investigate whether peripheral plasma profiles of pregnancy specific protein B (PSPB) are predictive of pregnancy outcome in adolescent sheep in which growth of the placenta has been compromised by the competing nutrient demands of maternal tissue synthesis. Embryos recovered on day 4 after oestrus from adult ewes inseminated by a single sire were transferred in singleton to prepubertal adolescent recipients. After transfer, the adolescent recipients were individually offered a high or low proportion of a complete diet to promote rapid (RMG) or normal (NMG) maternal growth rates (n = 12 per group). After day 100 of gestation the feed intake of the NMG group was adjusted weekly to meet the nutrient requirements of the gravid uterus. Blood was sampled three times a week throughout gestation and analysed for PSPB and progesterone. Liveweight gain during the first 120 days of gestation was 229 +/- 9.1 and 105 +/- 3.9 g day-1 for the RMG and NMG groups, respectively. For ewes delivering live young, mean placental mass at term was 263 +/- 16.8 and 438 +/- 44.6 g (P < 0.002), while lamb birthweight was 2.74 +/- 0.25 and 4.34 +/- 0.27 kg (P < 0.001) for the RMG (n = 8) and NMG (n = 11) groups, respectively. The biphasic pattern of PSPB secretion during gestation was similar in all ewes delivering live young, but individual concentrations within treatment groups were highly variable. Mean PSPB concentrations were lower in RMG than in NMG ewes throughout gestation (P < 0.05) and the major differences in relative terms were detected between days 50 and 100 of pregnancy. PSPB concentrations during this latter period were correlated (P < 0.05) with placental mass at term but not with lamb birthweight. High dietary intakes, leading to rapid maternal growth rates were associated with low peripheral progesterone concentrations (P < 0.02) throughout gestation. Irrespective of treatment group, progesterone concentrations during the second half of pregnancy were positively associated with both placental mass at term (P < 0.002) and lamb birthweight (P < 0.01). The incidence of non-infectious abortion during late gestation (125 +/- 1.3 days) was higher (P < 0.001) in the RMG (4 of 12) than in the NMG (1 of 12) group and was associated with abnormal PSPB profiles in the former group. The mass of the fetus at the time of abortion was highly correlated (P < 0.01) with mean PSPB concentrations up to day 120 of gestation, but was independent of peripheral progesterone concentrations. These results suggest that sequential measurement of PSPB may provide a reliable indicator of fetal distress and adverse pregnancy outcome in singleton bearing ewes. PSPB and progesterone analysis may also have prognostic value as a biochemical marker of suboptimal placental growth and function in sheep.