To clarify the mode of inheritance of alcohol dehydrogenase (ADH) isozymes in Echinochloa crus-galli, we induced single-banded mutant lines for ADH by gammaray irradiation; the irradiation of the 5-banded E. crus-galli var. formosensis (phenotype A 1 A 2 A 3 A 4 A 5 ) produced two single-banded mutant lines, A 1 and A 5 . All pairwise reciprocal crosses were made among the single-banded mutant lines and the naturally occurring single-banded type E. crus-galli var. praticola that displays only band A 3 . The ADH zymograms from the resulting F 1 progenies were identified by polyacrylamide gel electrophoresis and the relative staining densities of the bands were determined by densitometer scanning for several important E. crus-galli phenotypes and F 1 individuals. All F 1 seeds displayed both parental bands plus an additional band located intermediate to the parental bands. Moreover, the ratios of the band densities were in agreement with those expected from the kinetics of ADH dimer formation. The results can be accounted for by three loci encoding three ADH subunits. Also, the data indicate that the A 3 band of the 5-banded phenotype consists of two different dimeric products, homo-and hetero-dimers.