Gloeosporium limetticola Clausen, the causal fungus of withertip disease, was readily isolated from infected lime ( Citrus aurantifolia) leaves. Good growth was obtained on 2 % potato dextrose agar, but isolates lost their ability to produce spores after one or two transfers on this medium. Sporulation could be induced, however, by subculturing to sterile lime stems. Symptoms of withertip were reproduced in the laboratory by inoculating detached lime shoots and leaves with spore suspensions prepared from cultures or with disks of mycelium. When spore suspensions were used a high concentration, 10 6-10 7 spores/ml., appeared to be necessary to obtain infection. Age of leaf appeared also an important factor limiting infection and this is possibly linked with the development of the cuticle. Spore germination on young lime leaves commenced within 2 hr. and was completed by the formation of an appressorium in 7–8 hr. The resistance to infection by G. limetticola shown by mature lime leaves and young leaves of certain other Citrus spp. was not directly related to any inhibition of spore germination. The behaviour of G. limetticola is briefly compared with that of Colletotrichum coffeanum Noack, causing coffee-berry disease in Kenya.