Two patients suffering from Brill-Zinsser disease were treated with azithro
mycin, which did not prove effective. Rickettsia prowazekii, the agent caus
ing Brill-Zinsser disease, cannot be treated with azithromycin. Both patien
ts had epidemiological features consistent with and a clinical course typic
al of the disease. The diagnosis of Brill-Zinsser disease was serologically
confirmed.