Experiments on the biosynthesis and microbiological conversion of indole alkaloids in Penicillium concavo-rugulosum were carried out with the growing and resting mycelia, respectively, of a selected strain of the same mold. The former experiments were performed by the use of DL-tryptophan-3-14C or DL-mevalonic acid-2-14C-lactone as a precursor, while the latter experiments by the use of rugulovasine A-3H, dihydrorugulovasine A-3H, 4-[γ, γ-dimethylallyl]-tryptophan-3H, chanoclavine-[I]-3H or the other tritilated ergoline alkaloids. The results of these experiments suggested that in the Penicillium mold employed there exist the following biosynthetic route: tryptophan+mevalonic acid→4-[γ, γ-dimethylallyl]-tryptophan→rugulovasine A→dihydrorugulovasine A→dihydrorugulovasine A-lactam.