Etiolated seedlings of Sinapis alba treated for 24 hours with 40 ÊM FdUrd become inhibited in elongation growth. 64 hours old seedlings only reach the same length as untreated plants of 48 hours. A comparison of untreated seedlings of 48 and 64 hours with inhibited plants of 64 hours fives the following results: The minimum stress relaxation time is the same for seedlings of the same size, whereas the extensibility is more dependent on the seedling's age. The total cell wall material content of the treated plants lies between the two controls, but the composition of the wall material (pectin and hemicelluloses) is not significantly changed by the treatment, only arabinose is significantly enhanced. From these results it can be concluded that FdUrd does not inhibit the growth by changing the formation or composition of the cell wall. The reduction of wall material is rather a consequence of the reduced growth.Key words: Sinapis alba, wall extensibility, FdUrd, growth inhibition, wall composition.