Objective: The purpose of this study was to determine if maternal serum concentrations of placenta growth factor (PIGF) and soluble Fins-like tyrosine kinase 1 receptor (s-Flt1) are more abnormal in patients with severe preeclampsia compared with mild preeclampsia. Study design: Serum samples were collected from 32 control patients and 80 patients with mild or severe preeclampsia. PIGF and s-Flt1 concentrations were quantitated by enzyme-linked immunosorbent assay (ELISA). Results are expressed as median (Q1-Q3) unless stated otherwise. After normalization, serum markers were compared using one-way analysis of covariance (ANCOVA). Results: Patients with preeclampsia had decreased levels of PIGF (75.1 +/- 14 vs 391 +/- 54 pg/mL, P < .0001) and elevated s-Flt1 concentration (1081 +/- 108 vs 100.1 +/- 26.9 pg/mL, P < .0001) compared with the respective controls (mean +/- SEM). PIGF concentration was lower in patients with mild preeclampsia compared with severe, respectively (67 pg/mL [39-158] vs 24 pg/mL [4-57], P < .02). s-Flt1 was not different between mild and severe preeclampsia (674 pg/mL [211-1297] vs 1015 pg/mL [731-1948], P = .08). Conclusion: PIGF and s-Flt1 serum levels are abnormal in patients with preeclampsia compared with controls, but only PIGF is more abnormal in severe preeclampsia compared with mild preeclampsia. (c) 2006 Mosby, Inc. All rights reserved.