Coagulation factor concentrates prepared in England are all subjected to heating in solution or in the lyophilised state. Concentrates of factor VIII, factor IX (II and X), factor VII and factor XI are terminally heated in the lyophilised state at 80 degrees C for 72 h but the current fibrinogen concentrate withstands only 70 degrees C for 24 h. 33 patients receiving factor VIII concentrate (code 8Y) and factor IX concentrate (code 9A) for the first time have had regular liver function tests (LFTs) and we have at least some data on 26 of them exposed for greater than 3 months. Of these 26 patients, four had received no blood products before 8Y, 15 had received only cryoprecipitate before 8Y, and seven had received no blood products before 9A. Nine have missed only one or none of their two-weekly tests, four have missed two or three tests and on the remaining 13, the LFT follow-up has been unsatisfactory, although in some cases clinical examination has been helpful. 12 batches of 8Y from greater than 70,000 donations and seven batches of 9A from greater than 40,000 donations have been used. In 13 patients who have had regular prospective LFTs, none has had an ALT or AST level above twice normal. One patient followed only irregularly has shown an isolated ALT rise at eight weeks, unconfirmed at nine or at 17 weeks.