The aims of this study were to determine the factors that influence blood donation in different demographic groups in a multi-ethnic, multicultural community, and to devise a strategy for a national campaign to increase voluntary non-remunerated blood donations. The majority (87%) of blood donations in Trinidad and Tobago are replacement donations. Seventy per cent of the country's transfusion needs are not met. In 1998, the World Health Assembly recommended that reliance on replacement donations should be phased out due to their association with an increased risk of transfusion-transmitted infections. An observer-administered questionnaire was completed by 1423 respondents in a multi-ethnic borough in central Trinidad. Respondents were classified as donors or non-donors and grouped by age, race, religion, employment status and highest level of education. The prevalence of a history of blood donation and the factors that encouraged donation or conversely discouraged donation in each demographic group were recorded. A total of 1146 (81.2%) respondents had never donated blood. Of the 277 (18.8%) who had previously donated, replacement for a family member or friend was the most common reason (86.9%). The prevalence of donation was low in all racial, religious, gender, educational and age groups. However, there were significant demographic variations. The majority (71.3%) of non-donors cited a lack of information as a major reason for non-donation and expressed a willingness to donate if access to information and donation facilities were improved. Voluntary blood donation in Trinidad and Tobago could be greatly increased by a national education campaign and increased accessibility to donation centres. This would ensure a safer and more reliable blood supply.