Relative changes of soil pectolytic Erwinia (PE) could be determined by using the enrichment technique, for which the field soil was enriched anaerobically in Meneley's medium at 28.degree.C for 24 hours prior to plating on crystal violet pectate (CVP) medium. The detected PE levels in the tobacco field soils in which hollow stalk pathogen had heavily infested tobacco in the previous year, were high from mid May to late June. They were low from mid July through early August. The PE levels were more unstable in the field which were not mulched than in mulched ones with polyethylene film, and they showed similar pattern as cumulative rainfall during the same period. The concentration of 2.75 x 10ex7 Erwinia carotovora subsp. carotovora (Ecc) cells per g of soil was required for inducing 50% soft rot (ED50) in tobacco seedlings (Burley 21) planted in pot with field soil. Soil inoculation with Ecc at tobacco transplanting time was effective to increase the occurrence of the disease. The PE population levels detected from the fields at transplanting time and a month later were positively correlated with the incidence of hollow stalk (r = 0.73*, r = 0.70*).