Two strains (pepty 695 and pur 221) of Claviceps purpurea have been used to study the dependence of proline turnover on incubation time (1, 3, 6, and 12 hours) under different culture conditions (synthetic saccharose-citrate medium NL 720 and complex wort medium M 107) by nieans of tracer technique.In the saprophytically ergotoxine producing strain pepty 696 the proline is utilized in the protein and alkaloid biosyntheses. On the other hand, under non-producing conditions (M 10) the radioactivity of proline-14C is incorporated into many fractions and finally into CO,. I n submerged culture (NL 720) the Claviceps strain pur 221 which does not produce ergolines uses proline only to a small extent in the protein biosynthesis, while most of this amino acid is not metabolized. The extent of uptake of proline is not correlated with the alkaloid synthesis.For comparison the turnover of ~-glutamate-'~C and ~,~-o r n i t h i n e -l -'~C by strain pepty 696Radiokohlenstoff aus den uniform niarkierten Vorstufen L-Phenylalanin, L-Alanin und L-Prolin wird spezifisch in die Tripeptidseitenkette der Peptidalkaloide von