Seed yield and some of its primary components, viz. primary and secondary branches, siliquae per plant, seeds per siliqua and seed size, were studied in the F1 and F2 populations of five intervarietal crosses of mustard. The parental cultivars represented a fairly wide range of variation for all the characters. Both additive and dominance components were important for these traits and the gene actions were dependent upon the particular cross combination involved. Degrees of dominance were variable within each trait and inconsistent over the generations. The estimates of broad sense heritability and genetic advance were moderate to high, indicating that direct selection on the basis of primary branches and seeds per siliqua would be successful in the early segregating generations. Only one group of genes was detected in these traits. None of the F1 hybrids were higher than the highest yielding cultivar 'Laha 101'. The production of hybrids higher than this cultivar is not possible without the introduction of genes from other sources.