Data on yield determinants, i.e. number of pods/plant and seeds/pod and 1000 seed weight, were collected and analyzed. Overall differences were significant for number of pods/plant and seeds/pod in field pea and 1000 seed weight in both crops. Separate analysis of variance also showed significant differences in most of the cases. Interaction effects of location, year and treatment were also significant for some of the traits. Faba bean in mixed cultures had lower numbers of pods/plant and seeds/pod and 1000 seed weight compared to the corresponding sole cultures, indicating that the relative yield reduction in faba bean under mixed cultures could be the result of an additive effect of small individual reductions in all determinants. The relative advantage in field pea seems to be an additive effect of small individual increases in seed size and number/pod. Strong positive association between performances under the two systems for all yield determinants in both crops indicated selection of better genotypes for these traits under any system could inadvertently identify better genotypes regardless of the system. Grain yield was positively associated with number of pods/plant in faba bean and all determinants in field pea, indicating that selection for larger number of pods/plant in both crops and number of seeds/pod and seed size in field pea could improve productivity under mixed cultures, other determinants kept constant. Improvement in 1000 seed weight in faba bean could result in a negative selection for grain yield, indicating that a compromise for grain yield must be made or a minimum standard must be set for grain yield while selecting for larger seed size or separate breeding programs for seed size and grain yield must be followed.