Abstract Body: Introduction: Preeclampsia (PreE) is the new onset of hypertension following the 20^th week of gestation that is associated with inflammation, reduced fetal weight, hypertension and a progesterone deficiency. Progesterone induced blocking factor (PIBF) is an important protein whose production is stimulated by progesterone and plays a role in maintaining a healthy pregnancy. It suppresses NK cell activation, lymphocyte proliferation and inflammation, all of which have been shown to be increased in PreE. Low levels of PIBF have been associated with pregnancy disorders. Currently, the only treatment option for preeclampsia is early delivery of the feto-placental unit, which contributes to premature births. Hypothesis: Thus, we hypothesized that PIBF treatment reduces inflammation and blood pressure in the Dahl salt-sensitive (Dahl SS) rat model of PreE. Methods: To test this hypothesis, PIBF (2.0 µg/mL) or saline (vehicle) was administered intraperitoneally on gestation day 15 to Dahl SS and Sprague Dawley rats (SD, normal pregnant rats). On GD18, carotid catheters were placed for mean arterial blood pressure (MAP) measurements on GD19 and blood and tissue samples were collected. Results: Mean arterial blood pressure (MAP) was 105+2.2 mmHg in SD+ Vehicle rats (n=7),101+5.9 mmHg in SD+ PIBF rats (n=6), 138+2.7 mmHg in Dahl SS+ Vehicle rats (n=11), which significantly reduced to 118+3.1 mmHg in Dahl SS+ PIBF rats (n=10), p<0.05. Pup weight was 2.1+0.2 grams in SD+Vehicle rats, 2.2 +0.1 grams in SD+ PIBF rats, 1.3+0.1 grams in Dahl SS+Vehicle and significantly increased to 1.9+0.1 grams in Dahl SS+PIBF, p <0.05. Placenta weight was 0.5 +0.1 grams in SD+Vehicle rats, 0.5+0.1 grams in SD+PIBF rats,0.4+0.1 Dahl SS+ Vehicle rats and 0.6+0.1 in Dahl SS+PIBF. Pup/placenta ratio was 4.0+0.3 in SD+Vehicle rats and reduced to 2.7 +0.1 in in Dahl SS+Vehicle, p<0.05. PIBF treatment increased it to 3.4+0.1 in Dahl SS+PIBF, p<0.05. TNF-alpha levels were 19.6+ 7.2 pg/mL in Dahl+Vehicle rats (n=6), which decreased to 3.7+1.5 pg/mL in Dahl+ PIBF(n=6), p<0.05. Conclusion: Our findings demonstrate that PIBF ameliorates the maternal syndrome in the Dahl Salt-Sensitive rat model of PreE.