Abstract
The creatine sucrose agar originally described by Frisvad was modified by varying the sucrose and creatine concentrations and pH over a wide range. After extensive tests with commonly occurring species in Penicillium subgenus Penicillium, a new formulation was derived, which is termed neutral creatine sucrose agar. This medium produced eight different reactions among the 20 species tested, and hence has the potential to be a very useful taxonomic medium for species in this difficult subgenus.