When P. brevicompactum was grown between layers of dialysis membrane on Czapek-Dox agar for 3 days, no synthesis of mycophenolic acid, brevianamide A, asperphenamate or ergosterol occurred. After removal of the uppermost membrane layer, aerial mycelium developed and all 4 metabolites were formed. The bulk of the mycophenolic acid that was formed was excreted into the medium, the bulk of the brevianamide A and asperphenamate occurred in the aerial hyphae, and ergosterol occurred in both vegetative and aerial mycelia.