We studied gastrointestinal transit in a 57-year-old man with chronic intestinal pseudo-obstruction along with peripheral and autonomic neuropathy due to hereditary coproporphyria and we evaluated the effects of acute and chronic therapy with erythromycin. Noninvasive scintigraphic studies of regional transit of solid residue through the gut were obtained before treatment, during the acute i.v. administration of 500 mg, every-8-h doses of erythromycin for 24 h and after 15 weeks of oral therapy (500 mg, three times daily). During acute i.v. administration, symptoms and transit measurements dramatically improved; however, all parameters and symptoms returned to pretreatment levels during chronic oral therapy. We conclude that hereditary coproporphyria with associated autonomic neuropathy results in significant delay in small bowel and colonic transit; chronic administration of 500 mg three times a day oral erythromycin was not associated with maintenance of the improvement in regional transit and symptoms observed following acute i.v. administration of the drug at the same dose.