New antibiotics, pyrrolomycins F1, F2a, F2b and F3 were produced by Actinosporangium vitaminophilum sp. nov. when bromide ion was added to the fermentation medium. Addition of other halide ions such as chloride, iodide and fluoride ion showed no effect on pyrrolomycin production, affording polychlorinated pyrrolomycins A, B, C, D and E, but no F components. All four new antibiotics contain 2 approximately 4 mol of bromine, and their substitutional position was determined by X-ray analysis and synthesis, supported by spectroscopic analysis. They are strongly active against Gram-positive bacteria and fungi.