SUMMARYA convenient method for infecting Brassica seedlings in liquid medium with the phytopathogenic fungus Plasmodiophora brassicae was developed. The infection rates of two susceptible and two tolerant Chinese cabbage varieties with wild type P. brassicae were investigated. The content of free indole-3-acetic acid (IAA) was determined using combined gas chromatography-mass spectronnetry (GC-MS) with [^^Cg]-I-AA as internal standard during the first period of infection with the fungus (5-14 d) and compared with the indole glucosinolate content of two Chinese cabbage varieties (one tolerant, one susceptible) in tbe same developmental stages. The results showed that the mean of the IAA content in the infected plants was approximately 66-5 °(, bigber tban that of the non-infected controls. In botb the susceptible and tolerant varieties bigber levels of IAA were found in tbe infected plants 10 d after tbe beginning of incubation. After 14 d of incubation IAA levels decreased in tbe susceptible, infected plants and increased in tbe tolerant, infected piants.