To the Editor.— Rock et al 1 reported that in studies in 1982, the stated content of ampules of lyophilized antihemophilic factor (AHF, factor VIII) concentrates often exceeded the measured content, as assayed in the authors' laboratory. They stated that this discrepancy, with its implications of systematic undertreatment of classic hemophilia, has been corrected, an opinion shared by Lusher. 2 In our own experience, this is overoptimistic. The titers of coagulant AHF (factor VIII:C) in two ampules of the same lot of a commercial concentrate were 60% and 62% of that listed on the label. The ampules' expiration date was March 11, 1987, suggesting that this was a recent lot. I obtained the same result in an inadvertent blind study of our AHF assay in 1983, in which the local Red Cross and my laboratory assayed the same samples. My values averaged 58% of theirs ( P