ALTHOUGH the tocopherols, and in particular α-tocopherol, are widely distributed in Nature, they have not so far been identified in micro-organisms. The only micro-organism that has been adequately studied is bakers' yeast, which has been found to contain no tocopherol, although it contains another substance with vitamin E-like activity1. In view of recent work connecting α-tocopherol with some fundamental cellular processes, such as the reduced diphosphopyridine nucleotide-cytochrome c reductase system2, the regulation of succinate oxidation in rat liver mitochondria3 and the synthesis of adenosine triphosphate4, it was of interest to investigate the occurrence of tocopherols in a range of micro-organisms. The following organisms were grown in deep culture, using suitable media, the general composition of which is shown in Table 1: three strains of Esch. coli., 8196 and two vitamin B12-requiring mutants, N.I.R.D. and M200 (C181 strain) ; Streptococcus fœcalis R.; Bacillus cereus (strain 5) ; Staphylococcus aureus 4163; the nitrogen-fixing bacterium, Rhizobium leguminosarum 317 ; three sulphur-requiring, chlorophyll-containing bacteria, Chromatium 8379, Chlorobium thiosulphatophilum and Thiopedia; two chlorophyll-containing protozoa, Ochromonas malhamensis and Euglena gracilis; and one non-chlorophyll containing protozoan, Tetrahymena pyriformis.