The IgG anti-Toxoplasma western blot technique was used in 25 HIV-cases and 8 control sera from patients without HIV infection aimed at evaluating the humoral response in these patients. They were divided into 3 groups: 14 HIV positive cases with cerebral toxoplasmosis and IgG anti-Toxoplasma serological titers, 11 HIV positive cases without cerebral toxoplasmosis and with IgG anti-Toxoplasma titers, and 8 HIV negative patients with IgG anti-Toxoplasma titers. It was found that the higher the IgG anti-Toxoplasma serum titers are, the greater the number of bands in the western-blot is. The intensity of the bands measured by densitometry varied significantly for proteins of 66 and 31 kDa. According to the results, these proteins are of interest to evaluate their role in the reactivation of toxoplasmosis in HIV patients.