Seven cases of legionellosis were observed in a series of 81 renal transplant recipients. In the 6 patients with functional graft, pneumonia occurred 17 days on average after the beginning of transplant rejection treatment. The diagnosis was made by bronchoalveolar lavage: the direct immunofluorescence antigen technique was positive in 5 cases and culture in 6 cases. Legionella pneumophila sero-groups 5 and 1 were identified in one and 5 patients respectively. Six of the 7 patients were treated with ofloxacin. This fluoroquinolone was effective in all cases. It was administered as single therapy in 3 patients and did not interfere with ciclosporin A metabolism. Ofloxacin given in mean doses of 400 mg per day adjusted to renal function proved to be a simple, effective and well tolerated treatment of legionellosis in transplant recipients receiving ciclosporin A.