Sera from an epidemiological case-control study of leukaemias and lymphomas conducted between 1980 and 1986 were examined for reactivity to human herpesvirus-6 (HHV-6) by an indirect immunofluorescence assay. Statistical analyses of the data revealed higher HHV-6 seroprevalence and antibody titres in the cases, particularly evident in the disease subtypes acute myeloid leukaemia, Hodgkin's disease (HD), and low-grade non-Hodgkin's lymphoma. Within the control group alone, HHV-6 seroprevalence was placed at 55% at a serum dilution of 1:40. The controls also displayed higher seropositivity in females as compared with males. Further analyses suggest an association of increased HHV-6 seropositivity and geometric mean titre ratio with HD among young adults lacking social contact in the family group. This finding might indicate late exposure to HHV-6 in such persons and could possibly signify late exposure to a number of viruses, including those hypothesized as playing a role in the aetiology of HD. Previous reports have nominated Epstein-Barr virus as a possible candidate. Our results suggest that HHV-6 should be included in further investigations of the aetiology of HD.