Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used for their anti-inflammatory effects and have been shown to have chemopreventive effects as well. NSAIDs inhibit cyclooxygenase (COX) activity to exert their anti-inflammatory effects, but it is not clear whether their antitumorigenic ability is through COX inhibition. Using subtractive hybridization, we previously identified a novel member of the transforming growth factor-beta superfamily that has antitumorigenic activity from indomethacin-treated HCT-116 human colorectal cancer cells. On further investigation of this library, we now report the identification of a new cDNA corresponding to the thymosin beta-4 gene. Thymosin beta-4 is a small peptide that is known for its actin-sequestering function, and it is associated with the induction of angiogenesis, accelerated wound healing, and metastatic potential of tumor cells. However, only selective NSAIDs induce thymosin beta-4 expression in a time- and concentration-dependent manner. For example, indomethacin and SC-560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole] induce thymosin beta-4 expression whereas sulindac sulfide does not. We show that selective NSAIDs induce actin cytoskeletal reorganization, a precursory step to many dynamic processes regulating growth and motility including tumorigenesis. This is the first report to link thymosin beta-4 induction with NSAIDs. These data suggest that NSAIDs alter the expression of a diverse number of genes and provide new insights into the chemopreventive and biological activity of these drugs.