Twenty birdsfoot trefoil families were studied, first, to investigate variation in seed size and seedling vigor; second, to determine predictive values of parental performance; and third, to estimate heritability for combining ability. The experimental material consisted of open-pollination seed collected from 20 parents and 10 daughters of each. It was examined for seed size and was used for a seedling vigor test. Wide variation for both seed size and for seedling vigor existed both within and among families. The performance of the parents with respect to neither seed size nor seedling vigor was a valid indicator of the combining ability of the daughters. Heritability for these traits was low. In the discussion, the postulate was made that in selecting material for the Syn 0 generation of a new cultivar on the basis of combining ability, greater emphasis should be placed on additive gene action. The program would involve the selection of only those plants that, in addition to being high in combining ability themselves, had offspring with a high combining ability average.