This study aimed to determine the prevalence of anti-Toxoplasma gondii antibodies in patients with neoplasia. One hundred and eight patients with neoplasia. and 108 healthy controls were studied for the presence of anti-T. gondii antibodies using a micro ELISA and peroxidase-labelled anti-human IgG (rabbit) and IgM (goat). Anti-T gondii IgG antibodies were detected in 68 (63(.)0%) patients and in 21 (19(.)4%) of the controls, which was a statistically significant difference. In addition, anti-T gondii IgM antibodies were detected in seven (6(.)5%) patients and in one (0(.)9%) control. A high percentage of positivity for Toxoplasma antibodies in patients with neoplasia. was detected. Therefore, parasitological surveys of this patient group should be periodically performed.