The infection of Chinese cabbage (Braßica rapa ßp. pekinensis cv. Granaat) with the causal agent of the club root disease, Plasmodiophora braßicae Wor., leads to tumorous swellings of the root as a result of increased cell division and hypertrophy. An increased auxin formation in infected tißue by enzymatic hydrolysis of the precursor indole-3-acetonitrile has previously been postulated. Based on a recently published nitrilase cDNA sequence of Arabidopsis thaliana, we have amplified a partial nitrilase cDNA fragment from Chinese cabbage Lstrand cDNA, synthesized from hypocotyl total RNA, by polymerase chain reaction. Also, genomic nitrilase fragments from Chinese cabbage and Braßica oleracea, another host for P. braßicae, were amplified with the same set of primers. Sequence comparisons indicate high homology in exon and intron regions. The sequenced isoform of Chinese cabbage is most closely related to the NIT isoforms 1 and 2 of A. thaliana. Using the homologous nitrilase cDNA fragment (504 by of coding region) as a probe, nitrilase mRNA was determined in total RNA from P. braßicae-infected and healthy root tißue of Chinese cabbage. In both tißues a mRNA of approx. 1.3 kB was detected with similar amounts in infected and healthy tißues. Our results suggest that the biotrophic pathogen P. braßicae does not affect expreßion of NIT 1/2-related nitrilase(s) at the transcriptional level.