['Chloroquine, an alkalinizing lysosomotropic agent, enhances the intracellular activity of antibiotics against Mycobacterium tuberculosis or Coxiella burnetii.', 'To determine if chloroquine modifies the activity of clarithromycin, less effective at acidic pH, against intracellular Mycobacterium avium.', 'The activity of clarithromycin (4 micrograms/ml) against the MO-1 strain of M. avium was evaluated within human macrophages in presence of chloroquine (5 micrograms/ml). The minimal inhibitory concentration of clarithromycin for the strain was 2 micrograms/ml.', 'While clarithromycin alone did decrease the intracellular infection at day 7 of culture (P < 0.01), chloroquine alone did not impede the intracellular growth of M. avium, and did not enhance the activity of clarithromycin.'] Does chloroquine enhance the activity of clarithromycin against multiplication of Mycobacterium avium within human macrophages?