Evaluation of the immunogenicity and reactogenicity of two different formulations of commercially avail-able influenza vaccines in 4 different groups of immunocompromized outpatients (HIV positive patients, patients suffering from rheumatologic diseases and receiving treatment with immunosuppressive drugs and patients undergoing hemodialysis or continuous ambulatory peritoneal dialysis). The aim of the study was to investigate if the newest formulation of influenza vaccines (virosomal vaccines) offer a benefit in immunocompromized patients in comparison to an older subunit formulation.