Abstract Allozyme variation of eleven heterozymes of nine enzymes was analyzed for fourteen annual brome species in the type section of the genus Bromus with the use of PAGE. Diploids B . japonicus and B. squarrosus had identical zymograms, providing new evidence about their very close genetic relationships. Tetraploids B. secalinus and B . commutatus had very similar enzyme phenotypes, indicating their strong genetic affinity, but still differed in PRX-F homoeozymes of one composite genome. Diploid B. alopecuros appears to be the donor of one genome in the tetraploid B. lanceolatus . Bromus pseudosecalinus could not be one of the diploid progenitors for B . secalinus . 6-PGD gene is duplicated and diverged in several diploids of the section Bromus. All tetraploids studied exhibited different fixed heterozygosities of several heterozymes, suggesting their alloploid nature.