A field study was undertaken to investigate plasma protein electrophoresis (PPE) and serum amyloid A (SAA) concentrations at 1, 3 and 7 days of age in foals born by oxytocin-induced (group A, n =17) or spontaneous (group B, n =12) parturition. The putative diagnostic role of PPE and SAA in four septicaemic foals was also examined. At birth, beta-gamma-globulins were higher in group B, and then increased in both groups, probably due to colostrum intake. At day 3, no significant differences between the groups were detectable. In both groups, SAA values increased from day 0 to day 3, then decreased at day 7. Septicaemic foals had decreased concentrations of many electrophoretic fractions (probably reflecting decreased colostrum intake and circulating bacterial proteases) and an increased SAA concentration. It was concluded that both PPE and SAA concentrations vary with age and type of foaling and may be useful in the early diagnosis of neonatal septicaemia.