An Unusual Inhibition of an Anti‐P 1

Tests for unexpected antibodies using commercially prepared red blood cells demonstrated no agglutination even though crossmatching and testing with saline washed commercially prepared reagent red blood cells identified an anti‐P 1 . This antibody was inhibited when tested with red blood cells suspended in a modified Alsever's solution and several commercially prepared reagent red blood cell diluents. The inhibitory substance was identified as inosine. Hypoxanthine, adenine, and thymine also inhibited the anti‐P 1 . Partial inhibition was produced by uracil, 5‐methylcytosine, and xanthine. No other example of anti‐P 1 has been found to exhibit this unusual inhibiting characteristic.