Perinatal mortality in Victoria, Australia: role of group B Streptococcus. Group B beta-hemolytic streptococcus is the most common infective cause of neonatal morbidity and mortality. It is therefore surprising that no agreement exists for an approach to its prevention. There is also increasing evidence that occult infection may play an etiologic role in premature rupture of the membranes and preterm labor. In this report we review the role of group B beta-hemolytic streptococcal sepsis as a cause of perinatal wastage in the state of Victoria, Australia during the period 1982 to 1987. Group B beta-hemolytic streptococcus accounted for 1.7% of overall perinatal deaths, and for 30.3% (77 of 254) perinatal deaths directly attributable to infection. By comparison, over the same 6-year period, erythroblastosis accounted for 0.5% of perinatal wastage and there were only two deaths as a result of congenital syphilis. The true incidence of lethal group B beta-hemolytic streptococcal infection is probably greater because of the absence of histologic and bacteriologic studies in many perinatal deaths. We believe that intrapartum chemoprophylaxis with penicillin of all group B beta-hemolytic streptococcus-positive carrier mothers would significantly reduce neonatal morbidity and mortality from this cause. 