AIM: To investigate the effects of luminal exposure to H2O2 and two related thiol oxidizing agents on basal and stimulated chloride secretion in native colon using electro- physiological and pharmacological approaches. METHODS: Unstripped rat distal colon segments were mounted in Ussing chambers. Potential difference, cal- culated resistance and short-circuit current across un- stripped colon segments were monitored with a dual voltage/current clamp. Paracellular permeability was assessed by measuring the mucosa-to-serosa ? ux of a ? uorescent probe (FITC). RESULTS: Luminal exposure to hydrogen peroxide tran- sitorily stimulated chloride secretion without altering bar- rier function. This stimulatory effect could be blocked by basolateral atropine but not indomethacin. The cysteine and methionine oxidizing compounds, phenylarsine oxide and chloramine T respectively, mimicked the effect of H2O2, except for a drop in transcolonic resistance after 30 min. In contrast to the observed stimulatory effect on basal secretion, cAMP-stimulated electrogenic ion trans- port was blunted by luminal H2O2. However, the Ca2+- activated response remained unchanged. CONCLUSION: H2O2 may be an important selective modulator of intestinal ion and water secretion in certain pathologic conditions such as in? ammation or ischemia- reperfusion by multiple mechanisms. AIM: To investigate the effects of luminal exposure to H2O2 and two related thiol oxidizing agents on basal and stimulated chloride secretion in native colon using electro- physiological and pharmacological approaches. METHODS: Unstripped rat distal colon segments were mounted in Ussing chambers. Potential difference, The cal- culated resistance and short-circuit current across un- stripped colon segments were monitored with a dual voltage / current clamp. Luminal exposure to hydrogen peroxide tran- sitorily stimulated chloride secretion without altering bar-rier function. This stimulatory effect could be blocked by basolateral atropine but not indomethacin. The cysteine ​​and methionine oxidizing compounds, phenylarsine oxide and chloramine T respectively, mimicked the effect of H2O2 , except for a drop in transcolonic resistance after 30 min. In contrast to the observed stimu latory effect on basal secretion, cAMP-stimulated electrogenic ion trans- port was blunted by luminal H2O2. However, the Ca2 + - activated response remained unchanged. CONCLUSION: H2O2 may be an important selective modulator of intestinal ion and water secretion in certain pathologic conditions such as in? ammation or ischemia- reperfusion by multiple mechanisms.