We performed a prospective multicentre study to evaluate the efficacy of therapeutic strategies currently used for ocular toxoplasmosis in a large number of patients (n = 106). Treatment was given for at least four weeks and consisted of three triple drug combinations: group 1, pyrimethamine, sulphadiazine and corticosteroids (n = 29); group 2. clindamycin, sulphadiazine and corticosteroids (n = 37); and group 3. cotrimoxazole (trimethoprim and sulphamethoxazole) and corticosteroids (n = 8). Patients with peripheral retinal lesions remained without systemic therapy (group 4, n = 32). Patients from group 1 received leucovorin 5 mg twice a week. No difference in the duration of inflammatory activity was observed between the treated and untreated patients or between the separate groups of patients. The most important factor predicting the duration of inflammatory activity was the size of the retinal focus itself, independently of the therapy given (P less than 0.05). We showed a reduction in size of the retinal inflammatory focus in 52% of the pyrimethamine patients as compared to 25% of untreated cases. However the most frequent side effects were also associated with pyrimethamine medication and included hematologic complications as thrombocytopenia and leucopenia despite leucovorin medication.