Coprogen production of Neurospora crassa was dependent on glucose, aspartate and iron contents as well as on initial pH of the culture media. Surplus iron and acidic pH hindered the production of coprogen as well as the transcription of the sid1 gene (NCU07117) encoding putative L-ornithine-N5-monooxygenase, the first enzyme in the coprogen biosynthetic pathway. High glucose (40 g/l) and aspartate (21 g/l) concentrations were beneficial for coprogen synthesis, but neither glucose nor aspartate affected the sid1 transcription. Moreover, efficient coprogen production was observed after glucose had been consumed, which suggested that N. crassa accumulated iron even in non-growing, carbon-starving cultures.