OBJECTIVE: To study the clinical significance of simultaneous determination serum contents of C-reactive protein(CRP) and sialic acid(SA) in the diagnosis and treatment of neonatal bacterial infection. METHODS: Serum levels of CRP and SA were simultaneously determined in the same sample in 52 neonates(ranging from day 1 to 1 week of life) with bacterial inf ection. RESULTS: The serum CRP level [(68.3±32.8)mg/L] significantly increased within 24 hours of infection compared with that in the non-i nfection neonates [(0.78±0.25)mg/L](P < 0.01).When the infection was pa rtially or completely controlled the serum CRP level decreased significantly(P< 0.01). The serum SA content within 24 hours of infection was increased, but it w as not s ignificantly different from that in the normal cases [(0.91±0.40)mmol/L]. It was gradually elevated and became significant at day 1～3 and day 4～7 of infection [(1.88±0.85) and(2.95±0.87)mmol/L,respectively](P < 0.01).Only when the infection was completely controlled did the serum SA content in infection neonates reduce to normal. CONCLUSIONS: The combined assay of serum CRP and SA contents is helpful in making an earlier diagnosis and proper treatme nt for neonatal bacterial infection.