The regulation of vitamin B12 and bacteriochlorophyll formation was studied in a facultative methylotroph, Protaminobacter ruber, classified as a non-photosynthetic bacterium. Vitamin B12 was formed at an almost constant level under various cultivation conditions, while bacteriochlorophyll synthesis was drastically influenced by the growth conditions. Addition of B12 and hemin to the medium and the change of culture conditions from light to darkness in the early growth phases stimulated the pigment synthesis, but no pigment was formed under the continuous illumination and the addition of chloramphenicol inhibited the pigment formation. delta-ALA synthase and delta-ALA dehydratase activities were demonstrated in P. ruber. delta-ALA synthase formation was induced when cultures were transferred from light to dark conditions, which promoted the bacteriochlorophyll formation. Bacteriochlorophyll-protein complex had an absorption maximum at 870 nm and a very small peak at 800 nm.