The effects of TNBS-induced inflammation on specialised, low threshold, slowly adapting rectal mechanoreceptors were investigated in the guinea pig. Methods: Under isoflurane anaesthesia, 300µl saline or TNBS (15mg/ml) in 30% ethanol, was instilled 7cm from the anal sphincter. Six or 30 days later, single unit extracellular recordings were made from rectal nerve trunks in flat sheet in vitro preparations attached to a mechanical tissue stretcher. Results: TNBS-treatment caused macroscopic ulceration of the rectal mucosa at 6 days which fully resolved by 30 days. Muscle contractility was unaffected by TNBS-treatment. 6 days post-treatment, responses of low-threshold rectal mechanoreceptors to circumferential stretch were increased, the proportion of afferents responding with von Frey hair thresholds 0.1mN and mechanoreceptor excitability in response to electrical stimulation were increased in TNBS-treated tissue suggesting increased sensitivity of the mechanotransducer. Mechanoreceptor function at 30 days post-treatment was in most cases unchanged. The inflammatory mediator prostaglandin E₂ (1µM) activated mechanoreceptors (6 days) in conjunction with contractile activity but capsaicin (1µM) failed to activate mechanoreceptors. Bradykinin (1µM) activated mechanoreceptors independently of contractile activity and responses to stretch were increased in the presence of bradykinin. Both capsaicin and bradykinin activated unidentified stretch-insensitive afferents independently of contractile activity. Conclusions: Mechanoreceptor function is modulated at 6 days post-treatment but not at 30 days suggesting a moderate increase in mechanoreceptor sensitivity in inflamed tissue but not after recovery. Other unclassified stretch-insensitive afferents are responsive to inflammatory mediators and capsaicin, and may be involved in aspects of visceral sensation.