AIDS: Research results to determine the best prophylactic regimen for Pneumocystis carinii pneumonia (PCP) are reported. Overall results from these studies indicate patients who are eligible for PCP prophylaxis should be advised to take double-strength trimethoprim/sulfamethoxazole (TMP/SMX) on a daily basis, a dosage found more effective than thrice-weekly. To handle problems with side effects, one study demonstrated the success of using a 6-day dose escalation method that allowed 80 percent of the participants to complete treatment for 6 months. Patients remaining intolerant to TMP/SMX have the options of using atovaquone (not yet FDA-approved for PCP prophylaxis) or aerosolized pentamidine (not approved for treatment of PCP), which have been shown to be safe and effective in PCP prophylaxis. Due to recent FDA reforms, the use of off-label drugs may increase, but patients and physicians are cautioned that problems with insurance reimbursement may develop.