To prevent posttransfusion viral hepatitis, screening of potential blood donors includes the measurement of serum alanine aminotransferase (ALT) levels. The current use of single system-wide ALT cutoffs to determine acceptability of a blood unit or donor may not be appropriate, since male and Hispanic blood donors have much higher rejection rates than other donors, based solely on ALT level. Serum ALT measurements from the Hispanic Health and Nutrition Examination Survey were used to confirm these ALT elevations within general population samples of Mexican Americans, Cubans, and Puerto Ricans. Until specific tests are available to detect all hepatitis viral infections, testing blood donors for ALT levels will likely continue. Health personnel should be cautious in their interpretation of "elevated" ALT levels in these Hispanic populations.