Liver abscess formation due to Fusobacterium nucleatum is rare. We describe an HIV-1 antibody positive man, with normal surrogate markers of cell-mediated immunity, who presented with F. nucleatum bacteraemia and liver abscess formation. He was found to have IgG2 subclass deficiency. This case illustrates the clinical importance of altered B-cell function in patients who are at an early stage of HIV disease. © 1992 The British Society for the Study of Infection.