Many fungi cause plant diseases resulting in the loss of billions of U.S. dollars a year due to crop-damage and post-harvest decay. Also, several fungi produce toxins that can be fatal to man and other animals. Contamination of corn with one toxin called aflatoxin, produced by the fungus Aspergillus flavus, costs farmers in the U.S. $100 million annually.

In humans fungi cause skin infections such as ringworm and athlete's foot, but they also cause several deadly diseases which can be hard to treat. Fungi that can cause life-threatening infections in people include Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans.

Most patients with deadly fungal diseases do not have a fully functional immune system. They may have leukaemia or AIDS or they may be taking drugs to suppress their immune system because of organ transplantation. Although there are drugs to treat fungal infections these drugs can have some nasty side-effects because they are often toxic to people as well as to fungi. Also, several fungi are now resistant to the available drugs and there is a desperate need for new and better antifungal agents.

Although we could not survive without the Fungal Kingdom, it also costs us billions of U.S. dollars every year and kills thousands of people.