Post-transfusion hepatitis (PTH) is not only one of the most serious but also one of the most frequent complications of blood transfusion. Theoretically, all six forms of hepatitis, hepatitis A, B, D (Delta), non A-non B (enterically transmitted, E), non A-non B (parenterally transmitted, P), and so-called "associated" hepatitides caused by other microbial and parasitic infections must be considered when discussing PTH, but in this paper the "associated" hepatitides will not be discussed. © 1990.