The aim of this study was to identify some of the factors that affected the implementation of the Expanded Program on Immunization (EPI) in the Local Government Area (LGA). The study covered the three communities in Calabar LGA. Data on vaccine-eligible children and pregnant women were sought with questionnaires; other information on technical and community aspects of the EPI was gathered with specially designed checklists. EPI coverage for most antigens increased between 70-100% in response to highly-organized immunization campaigns initiated in 1985. In subsequent years, up to 1989, similar campaign-induced responses to national, state and local campaign efforts were observed. In contrast, coverage levels attributable to routine immunization remained unsatisfactory. When tested with the Z-statistic using 1985 as the base year (p < 0.05), there was a significant difference between the proportion of eligible children and pregnant women who did not receive their full dose of immunization. Socio-logistic variables found to be important in EPI implementations included scheduling, health staff attitude, intersectoral collaboration, and health education. Lack of community participation was also found to be a crucial constraining factor. As community participation/involvement is critical in sustaining health programs, social marketing techniques are suggested for future use.