Summary Integration of Agrobacterium tumefaciens transferred DNA (T‐DNA) into the plant genome is the last step required for stable plant genetic transformation. The mechanism of T‐DNA integration remains controversial, although scientists have proposed the participation of various nonhomologous end‐joining (NHEJ) pathways. Recent evidence suggests that in Arabidopsis, DNA polymerase θ (PolQ) may be a crucial enzyme involved in T‐DNA integration. We conducted quantitative transformation assays of wild‐type and polQ mutant Arabidopsis and rice, analyzed T‐DNA/plant DNA junction sequences, and (for Arabidopsis) measured the amount of integrated T‐DNA in mutant and wild‐type tissue. Unexpectedly, we were able to generate stable transformants of all tested lines, although the transformation frequency of polQ mutants was c. 20% that of wild‐type plants. T‐DNA/plant DNA junctions from these transformed rice and Arabidopsis polQ mutants closely resembled those from wild‐type plants, indicating that loss of PolQ activity does not alter the characteristics of T‐DNA integration events. polQ mutant plants show growth and developmental defects, perhaps explaining previous unsuccessful attempts at their stable transformation. We suggest that either multiple redundant pathways function in T‐DNA integration, and/or that integration requires some yet unknown pathway. See also the Commentary on this article by Faure, 229: 2386–2388.