Patients with confirmed PCP are randomized into one of three treatment groups. Group A receives SMX/TMP. Half of group A receives dapsone placebo (placebo is an inactive substance) daily plus trimethoprim placebo; the other half receives clindamycin placebo plus primaquine placebo. Group B is given dapsone plus trimethoprim. Half of group B receives SMX/TMP placebo; the other half receives clindamycin placebo plus primaquine placebo. Group C is given clindamycin plus primaquine. Half of group C receives SMX/TMP placebo, the other half receives dapsone placebo plus trimethoprim placebo. Treatment lasts 21 days; dosages will be adjusted for patients weighing less than 50 kg and more than 80 kg. Patients with a history of intolerance to SMX/TMP for whom rechallenge is considered medically contraindicated may be randomized to one of the non-sulfamethoxazole-containing arms.