SUMMARYAfrican cassava mosaic virus (ACMV) was detected in cassava leaves by ELISA. Some normal constituents of cassava leaves interfered with virus detection but leaf extracts ofNicotiana benthamianadid not. The symptom pattern was determined early in the growth of a leaf and subsequently changed little. ACMV was found only in the yellow or yellow green areas of the mosaic pattern. Virus content of the leaves increased with increasing symptom intensity, but decreased with leaf age and ACMV was not detected in mature leaves. Most whiteflies were found on young growing cassava leaves and the number decreased progressively with leaf age. This distribution will aid both the acquisition and inoculation of the virus.