The records of 46 neonates with proven septicaemia were retrospectively studied. Patients could be divided in 2 groups: in group 1 (21 infants) a positive blood culture was obtained before one day of life; in group 2 (25 infants) a positive blood culture was obtained between days 1 and 28. The sensitivity of 9 chemical and bacteriological tests and the efficacy of the initial antibiotic treatment were examined in both groups. Of the 21 germs isolated in patients from group 1, 86% were Gram positive bacteria and 95% were susceptible to ampicillin. Of the 26 germs isolated in patients from group 2, 80% were Gram negative enteric bacteria and 86% were susceptible to cefotaxime. Bacterial tests (gastric aspiration, antigen detection, feces culture) had a better sensibility than biochemical tests (C reactive protein, orosomucoid, fibrinogen).