Laboratory culture of myxomycetes was recently investigated in our laboratories from the viewpoint of search for bioactive secondary metabolites. Fruit bodies of Didymium iridis, which were found on a dead leaf, were collected at Ochi-san, Fukui Prefecture, Japan, in July, 2002. The plasmodium of this myxomycete was mass cultured in the laboratory on agar plates with oatmeal. The harvested plasmodial cells were extracted with 90% aqueous MeOH and 90% acetone. The extract was subjected to silica gel column chromatography and HPLC to give a green pigment makaluvamine I (1, 4.3 mg) and a red pigment damirone C (2, 1.5 mg), which were identified by spectroscopic methods including ¹H and/or ¹³C NMR and FABMS. Isolation of these pyrroloiminoquinone pigments has previously been reported from a marine sponge Zyzzya fuliginosa, while makaluvamines A and B were isolated from the myxomycete D. bahiense previously.