Toxoplasmosis is a zoonosis of broad geographic distribution, being an opportunist infection mainly in AIDS patients. The incidence of serum antibodies of the type anti-Toxoplasma gondii is variable and growing according the different age groups. The laboratory test for the diagnostic of this disease, include the exam of the pathologic species as well as immunologic tests. Although the serum tests have limitations, they are still utilized in the Clinical Analysis laboratories. To improve the congenital toxoplasmosis diagnosis in AIDS patients, the polymerase chain reaction (PCR) and Nested-PCR have been utilized alternatively.To focus the occurrence of toxoplasmosis, considering the different techniques and shapes of point of views in the serological analysis.The antibodies (Ac) anti-Toxoplasma gondii of 2994 patients from the Santa Catarina Federal University Hospital, in the period from February 28, 1996 to July 28, 1998 were evaluated. This evaluation was accomplished by the Immunofluorescency Indirect reaction, which was confirmed by the ELISA method.The results showed that 41.91% of the patients had the antibodies anti-Toxoplasma gondii. From this total we concluded that 0.87% of these patients had the IgM in different titles which can be or not classified in the acute phase of the disease. This study demonstrates that the incidence of toxoplasmosis in our orment is relatively high. It shows too that in the identification of the acute process of the disease, the serologic tests can be added to a more sensible and specific techniques that allows the evidentiation of the microorganism thus contributing to a better diagnosis.