This was a prospective observational study of maternal insulin-like growth factor binding protein-2 and -3 and fetal growth in 141 pregnant women after 24 weeks gestation who were scanned and venesected fortnightly. Cases (birthweight <5th centile) were sub-divided into those with growth restriction due to placental dysfunction (n = 25) and normal small (n = 27) and there were 89 normally grown controls. Maternal binding protein-3 was measured by radioimmunoassay and the overall pattern of the binding proteins and their proteolytic modifications were assessed by Western ligand blotting and immunoblotting followed by densitometric analysis. In controls, there was no correlation between binding protein-3 and birthweight, and binding protein-3 was elevated in the normal small but not the placental dysfunction group. Complete proteolysis of the 40 kDa doublet of binding protein-3 was observed in all pregnancies. Maternal serum binding protein-2 concentrations were unchanged in normal pregnancy compared to non-pregnant controls but elevated in the growth-restricted group and in all pregnancies binding protein-2 was predominantly present as a 14 kDa proteolysed fragment. These results suggest that compensatory changes in binding protein-2 and -3 or their proteolysis do not increase bioavailability and so do not confound the low maternal insulin-like growth factor-I in growth restricted pregnancies.