We studied the effects of minocycline, a semisynthetic tetracycline, on experimentally induced toxoplasmic retinochoroiditis in the rabbit. In two experiments we found that this drug effectively ameliorated the clinical disease and sterilized the ocular tissues from Toxoplasma organisms. Minocycline prevented death from toxoplasmic encephalitis in 75% of the animals, whereas all the control animals died of toxoplasmic encephalitis. Minocycline appears to be a promising agent for ocular toxoplasmosis.