Geotrichum candidum grew filamentously in batch culture. Hyphal fragmentation occurred during growth; mycelial fragments in the early part of the stationary phase had a mean length of 300 to 400 μm. The dry weight, total hyphal length, number of hyphal tips and turbidity of the culture all increased exponentially at about the same specific growth rate. The results suggested, the existence of a functional unit of growth consisting of a hyphal tip associated with a constant mean length of hypha. The hyphal growth unit was defined as the ratio between the total hyphal length and number of hyphal tips in the culture; for G. candidum this unit was about 100 μm long and its length remained constant when the organism's specific growth rate was varied by changes in temperature, carbon source or the incorporation of cycloheximide in the medium.