IS402, a transposable gene-activating element isolated on the basis of its ability to increase expression of the Tn1 bla gene in Pseudomonas cepacia, was cloned from pTGL52 into the vector, pBluescript KS+, and its nucleotide (nt) sequence was determined. This 914-bp element had terminal inverted repeats of 17 bp with a single mismatch, and upon insertion into Tn1 generated a direct target duplication of 3 bp. Comparison of its nt sequence with the GenBank and EMBL databases indicated that IS402 is unrelated to previously described bacterial IS elements.