Assignments of the 13C-nuclear magnetic resonance signals of eight naturally occurring chaetoglobosins were established. Incorporations of [1-¹³C]-, [2-¹³C]-, and [1,2-¹³C₂]-acetate, [¹³C-methyl]-L-methionine by Chaetomium globosum demonstrated that the molecules were formed from nine units of α acetate/malonate, three C₁ units, and one unit of tryptophan.