We studied G-CSF concentrations ([G-CSF]) at birth and their relationship with neutrophil count, incidence of infection, gestational age, labour, and the presence of maternal pregnancy-induced hypertension. Plasma [G-CSF] were significantly elevated in babies with suspected infection and in those of hypertensive mothers, compared to healthy babies delivered by elective caesarian section (median [range] = 3101 [75- > 5000] pg/ml and 153 [45-857] pg/ml versus 32 [11-266] pg/ml; P < 0.0001); and were unrelated to neutrophil count and gestational age. Initial high concentrations (> 100 pg/ml) declined by 7 d (P < 0.0001).