Receptor-like protein kinases (RLKs) are encoded by a divergent multigene family and their functions have been implicated in a wide range of signal transduction pathways. In this study, we examined the effect of salicylic acid (SA) on the expression of RLK genes in Arabidopsis thaliana. RNA gel blot analysis revealed that transcripts of RKC1 and a number of its homologs, whose translation products contain C-X8-C-X2-C motifs in the putative extracellular domain, accumulated to a higher level in response to SA treatment of plants. The chimeric fusion between the RKC1 5'-upstream region and the beta-glucuronidase (GUS) reporter gene reproduced the SA responsiveness in transgenic plants. In addition, some of RLK genes of the leucine-rich repeat (LRR) class and those of the S-domain class were also induced by SA. We found that the upstream regions of these SA-responsive RLK genes contain the TTGAC sequence, which has been suggested to be important for induced expression of many plant defense genes. These results suggest the involvement of a number of RLKs in SA-mediated defense responses.