A multicenter trial was conducted in Austria, Germany Holland and Switzerland. A total of 944 patients were included. They had a variety of diagnoses which required hospital admission and intravenous antibiotic therapy. The majority of patients (86.9 p.c.) started therapy with 200 mg doxycycline on the first day. All patients began therapy with an intravenous administration of doxycycline and most were later switched to an oral formulation. Various parameters of response were examined. Resolution of temperature as well as a decrease in associated pain was recorded. Side effects were usually mild and self limiting and were the reason to stop therapy in 1.2 p.c. of the patients. Early improvement was noted in the majority of the diagnostic categories. In 11 p.c. of the cases the response was not indicated or a poor response was noted but overall 89 p.c. of the patients responded to therapy. Doxycycline can be considered a truly useful hospital antibiotic in both its intravenous and oral forms.