Bangladesh began to hold National Immunization Days (NIDs) from 1995 as part of the country's goal to eradicate poliomyelitis by the turn of the century. The NIDs brought together government agencies, the media, voluntary organisations and individual volunteers in social mobilization and service delivery activities. This paper assesses the impact of the first two polio NIDs in terms of the immunization coverage and change in knowledge about the disease among women living in Dhaka city, the capital of the country. Data were collected through pre- and post-NID cross-sectional surveys in a sample of one area of Dhaka city which included slum and non-slum households. Knowledge data were collected from 525 women with at least one child aged less than five years. The oral polio vaccine (OPV) coverage during NIDs was obtained from 720 children. Knowledge of polio as a vaccine preventable disease increased after NIDs among both slum and non-slum women. The knowledge gap between the two groups was significantly reduced. Field workers, who regularly visit women at their homes to promote health and family planning services, were the main source of information for the slum women while television was cited as the most important source of information by non-slum women. The study revealed that 88% of children under five years received at least one dose of oral polio vaccine (OPV) during NIDs, and 67% received two stipulated doses with no significant differences between slum (65%) and non-slum (69%) groups. In addition, 68% of the children contacted during the NIDs were given vitamin A supplementation. The study suggests that strategies like NID can be effectively used to tap into community resources and to generate political commitments for health programmes.