OBJECTIVE To analyze gastrin and its precursors in plasma from mothers and preterm infants just after birth. METHODS 38 preterm infants, median (range) gestational age 32 wks (25-36 wks) and birth weight 1995 g (538-2764 g), and 29 mothers participated. Thirteen mothers were delivered by Cesarean section. The concentration of the total progastrin product was measured by a new processing-independent analysis (PIA) for progastrin, and the concentration of mature (i.e. alpha-amidated) gastrin was measured by conventional RIA. RESULTS The median concentration of the progastrin product was significantly higher than that of alpha-amidated gastrin in both mothers and infants (mothers: 40 versus 8 pmol/l; infants: 67 versus 9 pmol/l). The peptide concentrations were not correlated to sex, birth weight, umbilical cord pH, blood glucose concentrations or placenta weight. In mothers, the progastrin product was higher after multiple births than after a single birth. CONCLUSIONS As more than 90% of the total progastrin product in healthy nonpregnant adults is alpha-amidated, the results indicate that the biosynthesis of progastrin and its products is increased in mothers and even further in infants. Post-translational maturation is, however, markedly attenuated. Since it was recently suggested that progastrin and some of its non-amidated processing intermediates may act as growth factors for the gastrointestinal mucosa, the results of this study indicate that the gastrointestinal mucosa of pregnant women and infants is subject to gross gastrinergic growth stimulation.