Drought is a major abiotic stress that limits plant growth and crop productivity. A spontaneous wilty mutant (eibi1) hypersensitive to drought was identified from wild barley (Hordeum spontaneum Koch). eibi1 showed the highest relative water loss rate among the known wilty mutants, which indicates that eibi1 is one of the most drought-sensitive mutants. eibi1 had the same abscisic acid (ABA) level, the same ability to accumulate stress-induced ABA, and the same stomatal movement in response to light, dark, drought, and exogenous ABA as the wild type, revealing that eibi1 was neither an ABA-deficient nor an ABA-insensitive mutant. The eibi1 leaves had a larger chlorophyll efflux rate in 80% ethanol than the wild-type leaves; and the transpiration rate of eibi1 was more closely related to chlorophyll efflux rate than to stomatal density, demonstrating that the cuticle of eibi1 was defective. eibi1 will be a promising candidate to study the actual barrier layer in the cuticle that limits water loss of the plant. Exogenous ABA reduced leaf length growth in eibi1 more than in the wild type, implying an interaction on plant growth of ABA signal transduction and the eibi1 product. One may infer that the eibi1 product may reverse the growth inhibition induced by ABA.