Acute colonic pseudo-obstruction (ACPO) typically develops postoperatively or after severe illness. Studies suggest that pharmacologic manipulation with intravenous (i.v.) neostigmine (NSM) may be an effective and less invasive treatment modality for ACPO with minimal side effects. The purpose of this study was to retrospectively assess the efficacy and incidence of complications of an i.v. NSM bolus in patients with ACPO. Eight patients with ten episodes of ACPO were treated with a bolus dose of NSM. Rapid and effective decompression of the colon was achieved in six episodes after a single dose of NSM at a mean of 22.8 +/- 13.5 minutes. In three episodes decompression occurred after a second dose of NSM at a mean of 44.7 +/- 37.7 minutes. One patient failed NSM treatment but responded to a Cystografin enema. One patient experienced significant bradycardia. NSM is a simple, safe, and effective treatment for ACPO and based on result comparison of this study and previous studies both bolus and slow infusion dosing practices of NSM are effective. The NSM bolus dosing side effect profile has been shown to include significant bradycardia, whereas when NSM was infused over one hour significant bradycardic episodes requiring treatment have not been encountered. We propose that a prospective study evaluating NSM dosing as an i.v. bolus versus an i.v. infusion would be useful in determining whether NSM infusion can be proven safer than bolus dosing for the treatment of ACPO.