Studies on seed transmission of X. c. pv. phaseoli, cause of common and fuscous blight of Phaseolusvulgaris, were conducted in Uganda. P. vulgaris seed was the main source of primary inoculum. The population of X. c. pv. phaseoli in farmers', commercial and research seeds averaged 105-109 c.f.u./100 seeds; the levels of seed infection were 0.3-16.1%. There was a positive correlation between seed symptoms and the population of X. c. pv. phaseoli per seed. However, where seed was either slightly diseased or symptomless, X. c. pv. phaseoli did not increase P. vulgaris germination irrespective of population density. The min. population of X. c. pv. phaseoli required to initiate infection in the field was 102 c.f.u./seed while a 0.2% seed infection level resulted in serious disease incidence.