A case of congenital toxoplasmosis is reported in which the patient died at 32 days following seizures, coma and respiratory disturbances. Neuropathological examination showed numerous foci of softening throughout the brain. Histological examination disclosed widespread areas of inflammatory necrosis. Circumscribed areas of granulomatous inflammation were also found. Cysts containing a variable number of microorganisms and toxoplasmas free in the damaged areas were frequently observed. Small calcifications were scattered in the cerebral cortex and basal ganglia. Electron microscopy of postmortem brain specimens demonstrated toxoplasmas at various stages of development. The microorganism is enveloped by a two-layered membrane, the pellicle. Replication occurs in a vacuole inside the host cell. Following replication the newly formed parasites, the trophozoites, are released. Several replications without release may also occur with consequent cyst formation. The motile form of the toxoplasma, the tachyzoite, is fusiform with truncated cone shape of the anterior ending which is the presenting surface modified for host cell penetration. The modality of transplacental transmission and the clinical syndromes associated with toxoplasma infection are discussed. EM even of post mortem material contributes to knowledge of the structure of the parasite and of its life cycles.