In this investigation, we have determined the life span of the fruit bodies of Agaricus bisporus grown in a protected cultivation environment as 36 d. We describe the morphological changes occurring in ageing mushrooms and find that signs of senescence become visible around day 18; they steadily increase in amplitude towards the end of the fruit bodies' life. Cytologically, karyolysis and focal cytoplasmolysis were the first signs followed by indications of an increased permeability of the cytoplasmic membranes and by structural changes of the cell wall. These changes result in extracellular aggregations of the lytic cell remains encapsulating or bridging the hyphal cells. Cells of the stipe tissues were transformed to empty cylinders or had irregularly collapsed. Most basidia and subhymenial cells remained alive even on day 36. When the mushrooms were cultivated according to our usual growth procedures, about 50% of the fruit bodies were infected by Trichoderma harzianum and/or Pseudomonas tolaasii on day 18; all fruit bodies died on day 24 due to diffuse bacterial and mycotic infections manifesting themselves by tissue necrosis and discoloration of the caps and stipes. When none of the fruit bodies was harvested at the time of the first flush they soon formed a canopy of pilei and their growth ceased. On day 14, all these fruit bodies showed widespread mixed infections followed by a diffuse liquefaction necrosis of all tissues including the hymenium. Post-harvest fruit bodies kept at ambient temperature or at 2 °C at low r.h., or at 20° at high r.h. revealed a diffuse cell wall destruction which was followed by cytoplasmic degeneration in due course. Fruit bodies kept refrigerated had the least gross and cell structural changes during our observation period of 7 d. We conclude that the morphological changes occurring in post-harvest and in senescent fruit bodies of Agaricus bisporus are different.