An open, randomised study was performed to determine whether two doses of influenza vaccine were more effective than one to elicit an immune response in 70 patients with haematological malignancies. The responses were not improved by two doses compared with one (influenza A virus serotypes H1/N1 18% vs. 22% and H3/N2 26% vs. 14%; influenza B 25% vs. 22%). The results were similar in patients with ongoing and discontinued therapy. Patients treated with monoclonal antibodies for lymphoma had very poor responses. We conclude that two doses of influenza vaccine do not improve the antibody response in patients with haematological malignancies.