As part of an effort to monitor the safety of global blood transfusion services, the World Health Organization circulates a questionnaire for use in a database on blood safety. In 1992, 67% of countries responding to the survey (100% of developed, 66% of developing, and 46% of less developed countries) were screening all blood donations for HIV antibodies and 87% of these countries (100% of developed, 92% of developing, and 63% of less developed countries) carried out supplementary testing to confirm positive results. All developed countries, 72% of developing, and 35% of less developed countries screen blood for hepatitis B surface antigen and 94%, 71%, and 48%, respectively, screen for syphilis. The primary reasons for inadequate blood testing are the cost of test kits and reagents and the unreliability of supplies. The proportion of safe donors is highest in systems where all donors are voluntary and nonremunerated--conditions that exist in 85% of developed countries but only 15% of developing and 7% of less developed countries. Blood safety would also be improved by more appropriate use of transfusions and the provision of alternatives such as saline and colloids. Other problems include insufficient blood supply (e.g., none of the less developed and only 9% of developing countries collect 30 units or more per 1000 population per year) and inadequate quality assurance in all aspects of preparatory testing.