Toxoplasma antigen and Toxoplasma immune complex were shown to induce increased production and release of acid hydrolases from macrophage cell line P388D in a concentration-dependent manner. Antigen concentrations of 10-50 microg/ml gave a 2-4-fold increase in the activities of acid proteinase, acid phosphatase, and phospholipase A2 compared with control cells without antigen. Results were similar for immune complex concentrations of 30-80 microg/ml compared with controls. No significant lactate dehydrogenase activity was detected in the culture medium, indicating that enzyme release was selective and not due to cell death. These results suggest that increased release of acid hydrolases may play a role in the inflammatory lesions observed in Toxoplasma encephalitis.