During recent years,Peronospora tabacinahas frequently been intercepted on leaves in lots of imported Greek oriental tobacco at ports of entry in China. The question arises whether such infected leaf debris can be a source of primary inoculum. The present study has examined the pre‐export viability ofP. tabacinaon stored Greek oriental tobacco. Firstly, basic experiments were done: (1) to find a suitable medium (2% Bacto (Difco) agar) forin vitrogermination ofP. tabacinasporangia; (2) to determine the optimum (15–21 °C), maximum (30°C) and minimum (2°C) temperatures for sporangial germination; (3) to devise a suitable method of inoculation for an infectivity test. Secondly, viability tests were done on stored Greek oriental tobacco harvested in 1986 and 1987.In vitrogermination tests and infectivity tests were conducted separately, according to microscopic grading of the apparent turgidity of sporangia and sporangiophores collected from lesions of infected tobacco leaves of different cultivars and crop years. The tests were maintained for a much prolonged incubation period as compared with the controls. Neitherin vitrogermination nor infectivity tests showed any sporangia to be viable. Further work is needed to determine what period of storage is rationally acceptable for both plant quarantine and commercial