Eight strains of Streptomyces were grown on media composed of dextrose, glycine, glutamic acid, small amounts of vitamin-free casein hydrolysate, K2HPO4, MgSO4, CuCl2 and 3 ppm each of Fe, Ca, Mn and Zn. The last 4 metals were arranged in all possible combinations so that the mycelial weights of each organism were determined on 16 media. Contaminating traces of metals were removed by treating the media with chromatographic alumina. Fe was the only metal that produced a marked increase in growth when present alone. Fe and Zn showed a strong positive interaction. The effect of Zn was favorable in all cases. The effect of Ca was mostly favorable. Mn had no effect on the growth of the organisms. The effect of Ca was studied in more detail on Streptomyces fradiae 3535 and it was observed that Ca caused a delay in lysis.