X-14667A and X-14667B are two novel polyether antibiotics produced by Streptomyces cinnamonensis subsp. urethanofaciens. The antibiotics are active in vitro against Gram-positive bacteria and exhibit high affinity for monovalent cations. In the course of our search for new polyether antibiotics, several strains of Streptomyces soil isolates have been found to produce two novel antibiotics which we designated X-14667A and X-14667B (Fig. 1). In this report we describe the taxonomy of the antibiotic producing cultures, fermentation conditions for antibiotic production, and biological and ionophore properties of these antibiotics. The isolation and structure elucidation of the antibiotics are described in the following paper.