Flomoxef is a new oxacephem of broad antibacterial activity. The compound is mainly excreted through the kidneys. Two dose finding studies in patients with various degrees of renal insufficiency revealed that the dosage of flomoxef has to be reduced exactly according to the renal function. Although the N-methylthiotetrazole group has been replaced by a hydroxyethyl group, an inhibitory effect of flomoxef on vitamin K metabolism persisted. This effect was, however, less pronounced than with latamoxef. Only patients with low vitamin K stores are endangered. For those in whom low vitamin K stores are suspected repeated controls of prothrombin time are advised during the treatment. In contrast to latamoxef the platelet system was not affected by flomoxef. With the exception of loose stools in some patients no other clinical side effects during treatment were observed.