Expansins are proteins that can confer extensibility in plant cells by modifying the cross-links between cellulose microfibrils and polysacchrides. Because they are present as multi-gene families, their various patterns of differential expression suggest that each expansin plays a specific role in growth and development. Here, we describe the expression of expansin genes in maize roots in response to stage of growth, hormone treatment, or environmental stimuli. ExpB2 was the most strongly detected, with its transcript level being much higher than any other expansin in the regions undergoing cell division and elongation. Indole-3-acetic acid, which generally inhibits root elongation, induced expression of Exp l, but repressed that of ExpB2. This auxin-induced alteration was negated by treatment with 1-aminoethoxyvinylglysin (AVG), indicating that transcript levels may be modified by auxin-induced ethylene biosynthesis. ExpB2 expression was also induced by wounding and gravistimulus treatments. Therefore, our results imply that ExpB2 plays a role in the elongation of maize roots, and may be also involved in plant responses to environmental stimuli.