Several 3-indolinone dimers have been isolated from EtOAc extracts of the fruit bodies of Collybia peronata (peronatin A [1] and peronatin B [2]) and Tricholoma scalpturatum (7-hydroxy-7'-methoxyperonatin B [3] and 7,7'-dimethoxyperonatin B [4]), and their structures have been determined by mass spectrometry and nmr spectroscopy. The compounds are formed in the fruit bodies as a response to injury, although small amounts may be present also in intact specimens. It is suggested that they are probably formed by oxidative coupling of the corresponding 3-indolinones.