Our isolate of Streptomyces griseoviridus, which produced three minor factors in addition to viridogrisein and griseoviridus, which produced three minor factors in addition to viridogrisein and griseoviridin, was more sensitive to the addition of L-proline than the type culture of Streptomyces griseoviridus (NRRL2427). Yield improvement of these minor factors was attempted by the so-called controlled biosynthesis with L-proline. Addition of L-proline increased the production of neoviridogrisein II in which allo-hydroxy-D-proline in viridogrisein was replaced by D-proline.