The antimalarial activity of chloramphenicol, a broad-spectrum antibiotic was studied in three Indian Plasmodium falciparum isolates having high or low sensitivity to chloroquine. The antimalarial activity was evaluated in 72 hours culture in the presence of various doses of chloramphenicol alone or in combination with a fixed dose of chloroquine added at a concentration that is well tolerated by parasites in vitro. Significant growth inhibition with chloramphenicol was observed at concentrations above 10 micrograms/ml in three isolates. However, an increase in the antimalarial activity of the compound at low concentrations in the range of 0.25-2.5 micrograms/ml has also been observed in the presence of chloroquine. Parasite growth was significantly inhibited in chloroquine resistant parasites. Use of chloramphenicol with chloroquine may be useful as a combination therapy to improve efficacy of the antimalarials and to retard the development of resistance to the individual components of the combination.