The influence of weak pulsed magnetic fields of low frequencies on the germination rate of Mycotypha africana was tested. This fungus grows as a mycelium (M-culture) or in a yeast-like form (Y-culture) depending upon culture conditions. 5 h and 24 h of field application enhanced the germination rate in a Y-culture up to 2 or 3 times at low intensity levels and decreased it up to a factor 4 at the intensity level "4". M-cultures exhibited the same reaction pattern after 5 h exposition and no effect after 24 h exposition. The Y/M ratio is shifted by low field intensities towards the Y-form. The occurrence of stimulation as well as retardation by neighbouring intensities is discussed.