Persons with HIV disease who are receiving AZT are at risk for PCP, toxoplasmosis, bacterial pneumonia, and other serious infections. It is therefore important to find drugs that can be given along with AZT to control these infections. Aerosolized pentamidine (PEN) has been shown to be useful in preventing PCP and is expected to lower the 2-year risk of PCP. Both sulfamethoxazole/trimethoprim (SMX/TMP) and dapsone probably also provide effective preventive treatment against PCP, and both may be useful in preventing toxoplasmosis and extrapulmonary pneumocystosis.