Abstract A description is provided for Sphaerotheca mors-uvae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Chiefly on Ribes grossularia , but not infrequent on other species of Ribes , e.g. R. alpinum, R. atropurpureum, R. aureum, R. fosekulatum, R. nigrum and R. rubrum (Blumer, 1967). DISEASE: American gooseberry miltew. The pathogen attacks the tips of young shoots, the leaves becoming covered on both sides with white mycelium which spreads over the whole shoot causing a serious check in growth. Leaves and berries in all stages are attacked. The disease first appears on occasional isolated infected leaf trusses at the early flowering stage in gooseberry and the invisible spread is very rapid (44, 3413). Severe infection reduces shoot growth and consequently the crop in the following year (45, 1440). In black currant, differentiation of flower buds may be affected, resulting in considerable reduction of the crop (45, 153). GEOGRAPHICAL DISTRIBUTION: Asia (Japan); Europe (Austria, Britain, Bulgaria, Czechoslovakia, Denmark, Finland, Germany, Hungary, Italy, Ireland, Netherlands, Norway, Poland, Rumania, Sweden, Switzerland, U.S.S.R.); North America (Canada, U.S.A.). CMI Map 16, ed. 2, 1964. TRANSMISSION: Wind-borne conidia. Cleistothecia remain on the twigs and may produce ascospores in the spring. On Ribes prossularia the fungus normally overwinters as mycelium in the dormant buds (47, 2773). On R. nigrum , however, the main sources of infection in spring are the ascospores, the fungus producing active cleistothecia (46, 3140).