The usefulness of the new antibiotic, lincomycin, was assessed on both bacteriological and clinical grounds. Of 3200 strains of staphylococci isolated from clinical material, only 40 were resistant to lincomycin. These 40 were all of the same phage type and in fact almost all represented different isolations of the same staphylococcus which had spread to cross-infect various patients. Sixteen of 22 patients with staphylococcal infections, nine of 14 with pneumonia, 15 of 17 with acute exacerbations of bronchitis and two patients with other bacterial infections recovered completely with lincomycin therapy. The only side effect was diarrhea in four of the 42 patients given the drug by mouth. The place of lincomycin in therapeutics seems to be principally in the treatment of chronic osteomyelitis and, in patients allergic to the penicillins, in the treatment of staphylococcal, respiratory and other infections for which penicillin is usually employed.