An isopropyl alcohol (IPA)-assimilating bacterium identified as a Arthrobacter sp. (named A. hyalinus) was found to produce large amounts of coproporphyrin III and uroporphyrin III from IPA. In contrast, several other type cultures belonging to Arthrobacter spp. produced only small amounts of porphyrins from glucose. Limitation of both dissolved oxygen and Fe salt was essential for the production of porphyrins by A. hyalinus. Zinc sulfate, MgSO4, Polypepton, yeast extract, L-glutamic acid and L-cystine stimulated the production of porphyrins, although an excess amount of L-cystine inhibited cell growth and porphyrin production. A mutant resistant against hydroxylamine and L-cystine produced 440 mg/l of coproporphyrin III and 195 mg/l uroporphyrin III mixed with a small amount of uroporphyrin I under the optimal fermentation conditions. Small amounts of penta-, hexa-, and hepta-carboxyl porphyrins (less than 5 mg/l were also produced.