The following non-specific indices of infection were studied in septicaemic and non-septicaemic babies: haemoglobin, total white blood cell count, differential white count, ESR, platelet count, C-reactive protein (CRP), serum immunoglobulins, plasma C3 and haptoglobin. Forty-three low-birthweight (LBW) infants with clinical features suggesting septicaemia were investigated; blood cultures were positive in 19 and negative in 24. The mortality was 53% in the culture-positive and 13% in the culture negative group. Comparisons between the two groups of babies showed that the CRP titre (measured by Latex agglutination) was the only reliable non-specific indicator of infection. The titre was elevated more often in culture positive (16/19) than culture negative (7/17) babies (P less than 0.001). The CRP titre (Mean +/- 2 S.D.) was 15.75 +/- 12 in blood culture positive and 6.13 +/- 11.72 in culture negative neonates respectively (P less than 0.0004). Positive CRP titres were found in 5 of 20 healthy controls (4 +/- 8.4). Sequential CRP titres showed a gradual decline with clinical improvement in both groups of patients. The IgM was unhelpful as it was raised (greater than or equal to 40 mg%) in 37 of the patients.