In an investigation on the post-harvest behaviour of cush-cush yams (Dioscorea irifida L.) grown at various locations in the French West Indies, the incidence of decaying tubers was ten per cent on average and occasionally ranging up to 37 per cent. Nearly eight out of ten rots were caused by the soil fungus Penicillium oxalicum Currie and Thom. Inoculation experiments indicated that the fungus gains an entry only through wounds. Rots almost always originate from the tail which is cut and spoiled with soil at harvest and no further contamination occurs during storage. Mycelial growth in vitro was greatest at about 25°C but rot extension was faster at 16 or 20°C than at 24°C or more; at l2°C a bacterial decay synergistically occurred. D. alata was less susceptible to P. oxalicum than D. caymensis and D. trifida, but no important difference was found among various cultivars of the last mentioned species.