Hepatitis C virus (HCV) genotypes were investigated in 57 HCV-infected patients undergoing allogeneic BMT at four European BMT units where death resulting from liver failure (LF) in HCV-infected patients varied from < 1% to > 80%. The aim of the study was to determine whether differing HCV genotypes could account for the different severity of post-transplant liver disease (LD). Sera from patients with pre (n = 22) or post-BMT (n = 35) HCV infection were collected from Italy (Genova, Monza), Sweden (Huddinge) and Germany (Ulm). Patients were grouped as follows: LF: 19/57; acute hepatitis (AH): 10/57 or chronic hepatitis (CH): 22/57; no liver disease (LD): 6/57. HCV genotypes were identified by hybridisation of the 5'UTR amplified products with type-specific oligonucleotides probes according to Simmonds (Hepatology 1994; 19: 1321-1324). Genotype HCV 1 was identified in 34 patients (60%), HCV 2 in 15 (26%), HCV 3 in three (5%), mixed infection in three (5%) and undefined in two (3.5%). In the LF group HCV 1 was identified in 10/19 and other genotypes in 9/19. Median timing of LF was earlier in patients infected with HCV 1 compared to other genotypes (45 and 68 days, respectively), largely due to the cause of LF; death from veno-occlusive disease (VOD) and hepatitis occurred at 30 and 68 days post-BMT, respectively. Genotype 1 was also identified in cases with no LD. These data indicate that there was no evident correlation between HCV genotype and type or severity of post-transplant liver disease.