Concentration of maize dwarf mosaic virus (MDMV) strains A and B were measured by the enzyme-linked immunosorbent assay (ELISA) in various tissues of grain sorghum grown under different environmental conditions. Virus titer was higher in plants at 15 C than at 25 C and much higher than at 35 C. Differences in light quality and intensity did not affect virus titer in either expanding or fully developed leaves. Plants grown in the controlled-environment chamber had more virus than those grown in the greenhouse. Under controlled environmental conditions, the youngest (top) leaf when one-third expanded contained much less virus than older plant parts. Virus titer increased slowly and reached a maximum in the fourth or fifth leaf from the top where it remained stable and did not decline sharply as has been observed for these viruses in maize. During grain filling there were moderate to high levels of virus in all parts of the plant including the head, but the virus disappeared from the grain and declined, particularly in the older leaves, as the plant approached physiological maturity. The sorghum hybrid, Bugoff, contained more virus than susceptible Zea mays ''Golden Cross Bantam'' and ''NE 28.''.