Background: In 1993, WHO and UNICEF recommended the administration of 0.05 mi doses of BCG, instead of 0.1 mi to newborns. This recommendation was adopted by the Chilean Ministry of Health, using the Merieux vaccine. Subsequently, different Health Services detected a high percentage of children without BCG scar at the time of their growth and development control. Aim: To assess the efficacy of BCG vaccination in a double blind randomized fashion, using two vaccine types and different closes. Patients and methods: Newborns of two public hospitals of Santiago were randomly assigned to receive the Tokio or Merieux BCG strains in doses of 0.05 or 0.1 ml. Ninety flue to 125 days after vaccination, vaccine scar was measured anti inmunogenicity was assessed using the tuberculin test. Results: Six hundred newborns (150 in each group) were included ill the protocol and results were assessed in 408. The percentage of children with a PPD reaction of 0 mm was 9.3, 3.7, 7.8 and 0% with the Merieux vaccine in doses of 0.1 mi Tokio vaccines in closes of 0.1 mi, Merieux vaccine in doses of 0.05 mi and Tokio vaccine in doses of 0.05 ml, respectively. In the same groups the scar diameters were 6.4 +/- 3.4, 7.3 +/- 2.7 5.6 +/- 2.8 and 7.3 +/- 2.9 mm. The observed differences for each group are significant, depending on the type of strain and dose, but favoring the Tokio type of vaccine. Conclusions: The BCG scar diameters obtained in this study are similar to those obtained in previous works in 1984 and 1986. This scar is the evidence of vaccination that nurses detect in health controls. Therefore the use of 0.1 doses for vaccination that result in better scars and PPD response, Is recommended.