A comparison was made of the results obtained with ciprofloxacin (750 mg/12 h) and doxycycline (100 mg/12 h), both administered p.o. for one week, in 34 and 36 patients respectively with Mediterranean spotted fever. Apyrexia was achieved after 50.1 +/- 34.2 h (mean +/- SD) of antibiotic therapy in the group of patients treated with ciprofloxacin and in 55.2 +/- 23.3 h in the group treated with doxycycline (no significant statistical differences). Resolution of the remaining signs and symptoms of the disease was achieved faster with ciprofloxacin. Both therapeutic regimens were effective and safe. Although more expensive than doxycycline, ciprofloxacin is a bactericidal compound which is better tolerated and has a lower risk of toxicity and of development of resistance. It can be considered, together with doxycycline, as an antibiotic of first choice in the treatment of Mediterranean spotted fever.