SUMMARYThe light absorption by living, uninjured mycelium ofAscochyta pisi, Pleospora herbarum, andPyronema omphalodeswas studied spectrophotometrically, using two specially devised methods. Differences between sporulating colonies exposed to near-ultraviolet radiation and nonsporulating colonies grown in darkness were evident, particularly inP. omphalodes.Exposed colonies showed increased absorption mainly in the region 300–350 mμ. Substances causing this increased absorption were located in irradiated vegetative mycelium ofP. omphalodesand possibly in the spores ofA. pisi.Absorption of 300–350 mμradiation by mycelium corresponds to one waveband of radiation (310 mμ) previously found to be very effective in inducing sporulation inA. pisi, P. herbarumandAlternaria chrysanthemi.