Societal perspective was used to analyze the cost and benefit of the current HIV-1 screening program in national blood donation centers in Taiwan. In addition, incremental cost-benefit analysis was performed to evaluate the combined HIV-1/HIV-2 screening program which may be implemented in the near future. The costs of the following items were estimated: enzyme immunoassay (ETA), confirmatory Western blot assay, disposal of the contaminated blood, marginal blood donor recruitment and follow-up of the HIV-1/HIV-2 cases found in the screening program. The benefits of the screening program included the saves of the following two aspects: cost of the medical care and the earnings loss of the transfusion-acquired HIV-1/HIV-2 patients. The discount rate of the benefit was set at 3% per year. The results showed that the total cost of HIV-1 screening in the national blood donation centers in Taiwan was NT$ 97,894,950 for 1,242,535 blood units in 1993. Since the screening program will prevent 43 cases of transfusion-acquired HIV/AIDS case, the total benefit was NT$ 133,663,077. Therefore, the benefit-cost ratio of HIV-1 blood screening program in blood donation centers in Taiwan was 1.37. The sensitivity and elasticity analyses showed that the most important factor affecting the projection is the specificity of the screening test. Finally, if the blood donation centers change their current screening test to combined HIV-l/HIV-2 EIA, the total incremental cost will be NT$ 13,433,120. To reach the break-even point of the incremental benefit-cost ratio, it requires at least 11 HIV-2 seropositive blood units found in the combined HIV-1/HIV-2 screening program.