Array-based comparative genomic hybridization (array-CGH) has powerful potential for high-throughput identification of genetic aberrations in cell genomes. We identified high-level amplification of kallikrein (KLK) genes, which are mapped to 19q13.3 and belong to the serine protease family, in the course of a program to screen a panel of urinary bladder carcinoma cell lines for genomic copy number aberrations using our in-house CGH-array. Expression levels of KLK5, -6, -8 and -9 were significantly increased in three cell lines with copy number gains of these KLK genes. Knockdown of these KLK transcripts by specific small interfering RNA significantly inhibited the invasion of a bladder carcinoma cell line through Matrigel in vitro. Reverse transcription-polymerase chain reaction analysis of 42 primary bladder tumor samples showed that increased expression of KLK5 was frequently observed in invasive tumors (pT2-pT4) (14.3%, 6/42) compared with superficial tumors (pTa, pT1) (0%, 0/42; P = 0.0052), and expression levels of KLK5, -6, -8 and -9 mRNA were higher in invasive tumors than in superficial tumors (P < 0.0001, P = 0.0043, P = 0.0790 and P = 0.0037, respectively). These observations indicate that KLK5, -6, -8 and -9 may be the most likely targets of the 19q13.3 amplification, and may play a crucial role in promoting cancer-cell invasion in bladder tumor.