Sepsis in the neonatal age is associated with risk factors for infections and with the immunological state of the newborn infant. BACKGROUND Verify if IgM and C-reactive protein were indicators of infection in newborn infants with risk factors. METHODS We studied 57 newborn infants that had: premature rupture of amniotic membranes associated ou no with clinical amniotics or with urinary tract infection. They were classified in three gestational age groups (< 34 weeks, between 34-36 6/7 and (37 weeks) Sepsis diagnosis was made through clinical and laboratorial criterious and we also included: IgM and C-reactive protein obtained of the newborn at birth and at fifth day of life. RESULTS Sepsis diagnosis was made in 18 (31.5%) of 57 newborn infants, 13 (22.8%) with early sepsis and 5 (8.7%) with late sepsis. The infection had statistical association with gestational age and with weight at birth. The gestational group < 34 weeks was more infected and in this group the number of newborn that died had association with infection. We did not observed association in the three groups studied between infection and sex. There were significant differences of levels of IgM between infected and not infected newborn infants in the same group of gestational age, this difference was more evident in the fifth day. There were association between levels of C-reactive protein > 10 mg/L and infection in the three groups studied. CONCLUSIONS C-reactive protein was the better indicator of infection at birth and in the fifth day of life and this was very important for the clinical evolution of the infection and in the late sepsis was the first prove that was altered.