Intestinal epithelial cells are constantly stimulated by reactive oxidant metabolites (ROMs) in inflamed mucosa. Monochloramine (NH2Cl), a cell-permeant ROM, is particularly relevant to the pathogenesis of inflammation in the gastrointestinal tract. Nuclear speckles, a unique nuclear subcompartment, accumulate a family of proteins, namely, serine- and arginine-rich (SR) proteins. They play important roles in regulation of pre-mRNA splicing. Currently, little is known about the link between inflammatory stimulation and the pre-mRNA splicing process, although gene expression is changed in inflamed tissues. The present study was designed to investigate whether stimulation of human colonic epithelial cells (HT-29 and Caco-2 cell lines) with NH2Cl affects nuclear speckles and their components. By indirect immunofluorescence, nuclear speckles have been shown to undergo rapid aggregation after NH2Cl stimulation. By utilizing Western blotting, SRp30 (a subset of SR proteins) in intestinal epithelial cells was found to be phosphorylated after NH2Cl treatment, whereas other SR proteins were not responsive to NH2Cl stimulation. The cytotoxic effect of NH2Cl was excluded by both negative lactate dehydrogenase assay and propidium iodide staining. Therefore, NH2Cl-induced morphological changes on nuclear speckles and phosphorylated SRp30 do not result from intestinal epithelial injury. Furthermore, the effect of NH2Cl on nuclear speckles and SRp30 was blocked by bisindolylmaleimide I, a selective PKC inhibitor. Together, the available data suggest that stimulation of intestinal epithelial cells with NH2Cl results in a consequent change on pre-mRNA splicing machinery via a distinctive signal pathway involving activation of PKC. This effect may contribute to oxidant-induced pathophysiological changes in the gastrointestinal tract.