THP-1 monocytoid cells, either not infected or chronically infected with human immunodeficiency virus type 1 (HIV-1), were challenged with Toxoplasma gondii. Parasitic growth, as assessed by trophozoite counting and measurement of supernatant p30 membrane antigen, was similar in HIV-infected and noninfected THP-1 cells. Also, T. gondii did not affect HIV replication. These experiments therefore failed to demonstrate any interaction between HIV-1 and T. gondii replication in concurrently infected monocytoid cells.