The WAG1 and WAG2 genes of Arabidopsis thaliana encode protein-serine/threonine kinases that are closely related to PINOID. In order to determine what roles WAG1 and WAG2 play in seedling development, we used a reverse genetics approach to study the wag1, wag2 and wag1/wag2 mutant phenotypes for clues. Although the wag mutants do not contain detectable amounts of the corresponding mRNA, they are wild type in most respects. However, wag1/wag2 double mutants exhibit a pronounced wavy root phenotype when grown vertically on agar plates, a phenotype observed in wild-type plants only on plates inclined to angles less than 90 degrees. The wag1 and wag2 mutants also demonstrate enhanced root waving, but to a lesser extent. Moreover, the double mutant roots are more resistant to the effects of N-1-naphthylphthalamic acid on the inhibition of root curling, raising the possibility that transport of auxin is affected in the wag mutants. Promoter fusions to the gusA reporter gene demonstrate that the WAG promoters are most active in root tips, consistent with the observed phenotypes in the wag mutants.