The discovery of terramycin, an antibiotic produced by Streptomyces rimosus, has only recently been reported,1yet an extensive clinical program is already under way to evaluate this new addition to the group of drugs useful in the treatment of infectious diseases. In vitro and in vivo studies indicate that terramycin has a wide bacterial spectrum2effective against both grampositive and gram-negative bacteria, certain of the rickettsias and viruses. It appears in many respects to be comparable to aureomycin in its antimicrobial activity. The drug is readily absorbed from the gastro-intestinal tract and produces significant and continuous blood concentrations when 250 mg. are given orally every six hours.2aIt is readily excreted by the kidneys and appears in the urine in an active state. The amount of terramycin excreted depends on the dose and varies from 10 to 35 per cent of the total amount of drug ingested.