Ellipsoidal arthroconidia of Geotrichum candidum produced in liquid medium with 5 g glucose 1 −1 as the carbon source contained about 20% (w/w) glycogen. When these were incubated at a concentration of about 1.5 × 10 6 conidia/ml in a glucose-mineral salts medium, 97% of the conidia germinated within 4.5 h. Under these conditions the glycogen content of the conidia remained constant. However, when they were incubated in a mineral salts medium without glucose, no germ-tube was formed even after 23 h incubation, although more than half of the glycogen content of the conidia was used during this period. Addition of glucose to cultures of these self-inhibited arthroconidia resulted in 95% germination within 3.5 h. During this germination the conidia very rapidly re-established a high endogenous glycogen content. It is suggested that glycogen is primarily used for maintenance energy.