A series of 33 analogues of the anti-Pneumocystis carinii drug 1, 5-bis (4-amidinophenoxy) pentane (pentamidine) was synthesized for screening against a rat model of P. carinii pneumonia (PCP). Twenty-five of the compounds showed efficacy against PCP when compared to a saline-treated control group. Two compounds, 1, 4-bis (4-amidinophen0xy) butane (butamidine, 6) and 1, 3-bis (4-amidino-2-methoxyphenoxy) propane (DAMP, 16), ...