Central nervous system toxoplasmosis was diagnosed in 12 immunosuppressed patients, eleven of whom had AIDS. Fever (9/12), confusion (7/12) and focal neurological manifestations (6/12) were the main clinical signs. Lumbar puncture yielded abnormal cerebrospinal fluid in 6/6 cases. Cerebral computed tomographic scan abnormalities, homogenous (2/12) or ring-like (9/12) contrast-enhancing mass lesions and/or low density lesions (6/12), were present in all patients. Brain biopsy confirmed T. gondii infection in 7/8 cases. The combination pyrimethamine-sulfadiazine accounted for complete resolution (4/8) or partial improvement (4/8) in eight out of 12 patients. Mean duration of therapy was 6.5 months (1-21.5 months) in 11 patients. No relapse was observed. In three cases spiramycin was ineffective in the prevention of neurotoxoplasmosis.