Ice nucleation-active (INA) bacteria active at -5 C were detected on leaves of Chinese cabbage in the field and in storage facilities in the Beijing Municipality. Populations of INA bacteria in the field and those on plants in storage were as high as 2.45 x 10(6) and 3.12 x 10(6) cfu/cm2 of leaf, respectively. About 93% of the INA bacteria isolated were identified as Pseudomonas viridiflava. Other species of INA bacteria isolated from Chinese cabbage included P. fluorescens and nonfluorescent pseudomonads. Chinese cabbage is a half-hardy species that risks exposure to several periods of subzero temperatures during its cultivation and storage in northern China and that may suffer serious postharvest soft rot. Under experimental conditions, no significant differences in frost damage were detected between chamber-grown plants inoculated with or free of INA bacteria. Frost sensitivity of Chinese cabbage was reduced significantly by hardening at 8 C for about 1 mo, although outer leaves of hardened plants remained somewhat frost sensitive. Frost-damaged Chinese cabbage leaf tissue was colonized and decayed more rapidly at 5 C by P. viridiflava than was non-frost-damaged tissue. The progress of soft rot could be inhibited by spraying leaves with a nonpectolytic strain of P. viridiflava 48 h before introduction of the pectolytic strain.