56 patients receiving chemotherapy for non-Hodgkin lymphoma or Hodgkin's disease with curative intent were monitored for up to one year after initiation of treatment. During chemotherapy (mean duration 5.2 months), 26 of the patients (46%) suffered from 38 febrile episodes. In only 16 instances was an extraoral cause for the septicaemia found. However, severe dental infection, reflected in an elevated radiological index for the jaws, was found more frequently in patients suffering febrile episodes than in those without (P = 0.02). Moderate to severe gingival inflammation was observed during 22 (58%) of episodes. During 71% of the episodes various pathological findings were also recorded in the oral mucosa. No source of infection other than an oral one was found in 42% of the patients. Our results emphasise the importance of oral foci as the possible infection source in patients receiving intensive chemotherapy.