A process for the preparation of a biologically pure culture of Claviceps fusiformis variant strain No. 00211, deposited on Nov. 15, 1981 at the National Collection of Microorganism, National Institute for Public Health, Budapest, Hungary, which comprises the step of culturing the Claviceps fusiformis strain No. 00164, deposited on May 2, 1977 at the National Collection of Microorganisms, National Institute for Public Health, Budapest, Hungary, in a solid culture medium containing sources of carbon, nitrogen, mineral salts, and agar as well as a barbiturate additive promoting the formation of cytochrome P-450, and isolating the colonies of the new strain No. 00211 by selection.