A process for obtaining metal-free corrinoids consisting of inoculating a culture media free of added compounds of metals of the VIIIth group of the Periodic Table with a parent strain of Rhodopseudomonas, cultivating under illumination, repeating the steps of inoculating and cultivating employing said culture media and said illumination employing a part of the sequential culture from the preceding stage as an inoculum in each subsequent state, for a series of several pre-production culture stages, inoculating said culture media with the preceding sequential culture for the last time, cultivating under illumination, separating the microorganism from the culture media of the production culture stage and isolating metal-free corrinoids from the culture media of the production culture stage.