BACKGROUND During pregnancy, mechanisms that allow for regulation of continuous fetal and placental vasculogenesis with prevention of maternal neo-vascularization remain elusive. The vascular endothelial growth factor (VEGF) biological system has a key role during vasculogenesis. The aims of this study were to validate a bioassay for soluble vascular endothelial growth factor receptors 1 and 2 (sVEGFR-1 and sVEGFR-2) in baboon plasma and to determine the maternal and fetal plasma concentration of these receptors at the end of the baboon pregnancy. METHODS Maternal peripheral blood samples were obtained from eight baboons (Papio anubis) prior to elective cesarean section and from the umbilical cord after the fetuses were delivered. Spike and recovery experiments at various concentrations in pooled baboon maternal plasma were used to validate a human quantitative sandwich immunoassay for sVEGFR-1 and -2. Concentrations of sVEGFR-1 and -2 were then determined in maternal and fetal plasma samples. RESULTS No significant correlations were observed between sVEGFR-1 or -2 concentrations in maternal and fetal circulations. The concentration of sVEGFR-1 was at least 30 times greater and that of sVEGFR-2 approximately two times greater, in maternal than in cord plasma (both P < 0.01). CONCLUSION These findings suggest that baboons can be used to study the regulation of vasculogenesis during pregnancy.