The interaction between headbugs (Eurystylus sp.) and grain mould (GM) on sorghum was examined in field trials carried out at Samaru, Nigeria in the 1995 and 1996 wet seasons. The results obtained show that in all three sorghum cultivars tested, insect damage increased the number of fungal colonies associated with the grain. This resulted in lower germination, 1000-grain mass and yield in such treatments. Insect damage also altered the relative abundance of the common fungal flora species as, following insect damage, Fusarium moniliforme (≡Gibberella fujikuroi), Phoma sorghina and Curvularia lunata (≡Cochliobolus lunatus) were the most common fungi in decreasing order of frequency as against the normal order of P. sorghina, F. moniliforme followed by C. lunata. These results are the first clear evidence of interactions between headbugs and GM in Nigeria.