Abstract A description is provided for Spiroplasma kunkelii . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Zea mays is the major natural host. Euchlaena mexicana and E. perennis are known experimental hosts and may be involved in the epidemiology of this disease. Various other plants have been infected by artificial inoculation using leafhopper vectors. e.g. Broad bean and Vinca rosea [Catharanthus roseus] using Euscelidius variegatus (57, 565) but these are probably not natural hosts. DISEASE: Corn/maize stunt. Infected maize is stunted and shows chlorotic stripes and often reddish purple leaf margins (69, 1042). Some plants have been found to be infected but show no symptoms. This is a major disease limiting maize production in tropical lowlands of America. GEOGRAPHICAL DISTRIBUTION: Widespread in tropical lowland America, from Texas in the north to the lowlands of Bolivia in the south (62, 166). Reports include USA: California, Florida (69, 1042), Michigan (Whitcomb et al. , 1986); Texas; Mexico (69, 1042); Jamaica (62, 2437); Nicaragua (67, 1283); Peru (66, 3773); Brazil (Paranfi, 65 4390) and possibly Venezuela with very low incidence (57, 133). TRANSMISSION: The principal vector is the leaf hopper Dalbulus maidis but other leaf hoppers, such as Euscelidius variegatus, Dalbulus longulus, Cicadulina and Baldulus spp., have been shown to acquire and transmit the pathogen experimentally (64, 160, 3831; 63, 1748, 5332). No other method of transmission has been found.