Pneumocystis carini pneumonia is a major cause of death in AIDS patients in the United States. The presently available treatments have limited use due to a high incidence of adverse reactions. Therefore, there is an urgent need for a safer method for treatment and prevention of this disease. Recent evidence has suggested that P. carinn is related to fungi and that the wall ofthe cyst form contains 1,3-13-glucan as a major constituent. Based on this, several proposed 1,3-f3-glucan synthesis inhibitors were evaluated for their ability to control P. carinu pneumonia in vivo. Compounds from two classes of 1,3-13-glucan synthesis inhibitors, the echinocandins and papulacandins, were found to be effective against P. carinii.Pneumocystis carinii pneumonia is the most prevalent opportunistic infection and a frequent cause of death in AIDS