In January 1994 alfalfa mosaic virus was reported for the first time on tobacco in Zimbabwe. The virus was identified from its field symptoms, and also from biological and serological assays. The infected plants had extreme chlorotic mosaic patterns on the leaves and showed vein-clearing when only the top leaves were infected. There were enations on some of the infected leaves. Sap inoculations caused chlorotic local lesions on Nicotiana glutinosa . The infected plants in the field were mapped and the proportion of infected leaves on each plant determined. These proportions suggest that the spread of the virus was initially from the primary infection site to a patch of 52 plants in the immediate vicinity, and subsequently to isolated individual plants or smaller patches. This distribution resulted from aphid transmission of the virus by: a) nymphs or apterae, resulting in the localised patch, and b) alates, resulting in the isolated plants and patches. The source of the virus is unknown, but other crops in the area include potatoes and paprika. The infection on the first plant probably took place in the field prior to active growth. The presence of the virus both increased the severity of alternaria brown spot and reduced the quality of the cured leaf.