Between Dec. 1, 1973, and May 30, 1989, 36 patients (37 eyes) with ocular toxoplasmosis seen at a uveitis clinic received quadruple therapy (pyrimethamine, trisulfapyrimidines, clindamycin and prednisone). The criteria for quadruple therapy were active lesions involving or threatening the macula or the optic disc, or a visual acuity of 20/70 or worse due to vitreous opacification caused by active inflammation. All but four of the cases showed improved vision. A total of 54% of the cases responded favourably within 2 weeks after the start of treatment, and 81% responded within 3 weeks. Patients took pyrimethamine for 1 to 2 weeks and received trisulfapyrimidines and clindamycin for 3 weeks, with a tapering course of orally given prednisone. The only complication was skin rash secondary to trisulfapyrimidine therapy, in four cases. None of the patients manifested diarrhea, pseudomembranous colitis or bone marrow suppression. The length of follow-up ranged from 1 month to 15.5 years. There were seven recurrences in five patients, five of which responded to a second course of quadruple therapy.