CRP, alpha 1-acid glycoprotein and haptoglobin were studied in 13 septic shock neonates. Endotoxin was recovered from eight infants. Serum cortisol concentration from infants with endotoxemia (917 +/- 596 ng/ml) was significantly higher than that from infants without endotoxemia (398 +/- 239 ng/ml). Serum cortisol correlated well with immature neutrophil counts defined as the unit "band/neutrophil". Increased cortisol level and immature neutrophil counts preceded the elevation of CRP, alpha 1-acid glycoprotein and haptoglobin in four extremely premature neonates. We conclude that positive interactions between endotoxin, cortisol and acute phase protein synthesis are present in the initial period of infection, and delayed acute phase protein synthesis is suspected in extremely premature neonates.